diff --git a/backend/package-lock.json b/backend/package-lock.json
index e877cc0..e5efdd0 100644
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
@@ -11,6 +11,7 @@
 			"dependencies": {
 				"@prisma/client": "^6.2.1",
 				"debug": "^4.4.0",
+				"decimal.js": "^10.4.3",
 				"dotenv": "^16.4.7",
 				"koa": "^2.15.3",
 				"koa-body": "^6.0.1",
@@ -661,6 +662,11 @@
 				}
 			}
 		},
+		"node_modules/decimal.js": {
+			"version": "10.4.3",
+			"resolved": "https://registry.npmjs.org/decimal.js/-/decimal.js-10.4.3.tgz",
+			"integrity": "sha512-VBBaLc1MgL5XpzgIP7ny5Z6Nx3UrRkIViUkPUdtl9aya5amy3De1gsUUSB1g3+3sExYNjCAsAznmukyxCb1GRA=="
+		},
 		"node_modules/deep-equal": {
 			"version": "1.0.1",
 			"resolved": "https://registry.npmjs.org/deep-equal/-/deep-equal-1.0.1.tgz",
diff --git a/backend/package.json b/backend/package.json
index a61bca6..b5d1d0b 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -26,6 +26,7 @@
 	"dependencies": {
 		"@prisma/client": "^6.2.1",
 		"debug": "^4.4.0",
+		"decimal.js": "^10.4.3",
 		"dotenv": "^16.4.7",
 		"koa": "^2.15.3",
 		"koa-body": "^6.0.1",
diff --git a/backend/prisma/migrations/20250111215310_init/migration.sql b/backend/prisma/migrations/20250111215310_init/migration.sql
new file mode 100644
index 0000000..ed190dc
--- /dev/null
+++ b/backend/prisma/migrations/20250111215310_init/migration.sql
@@ -0,0 +1,8 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `invoice_id` on the `InvoiceItem` table. All the data in the column will be lost.
+
+*/
+-- AlterTable
+ALTER TABLE `InvoiceItem` DROP COLUMN `invoice_id`;
diff --git a/backend/prisma/schema.prisma b/backend/prisma/schema.prisma
index 4c742d5..c4d92ec 100644
--- a/backend/prisma/schema.prisma
+++ b/backend/prisma/schema.prisma
@@ -48,7 +48,6 @@ model InvoiceItem {
 	item_quantity      Int
 	item_unit_price    Decimal  @db.Decimal(10, 2)
 	item_unit          String   @db.VarChar(50)
-	invoice_id         Int
 	invoice            Invoice  @relation(fields: [invoice_date, invoice_suffix_code], references: [invoice_date, invoice_suffix_code])
 
 	@@id([item_id, invoice_date, invoice_suffix_code])
diff --git a/backend/src/app.ts b/backend/src/app.ts
index d5efbdc..460ded3 100644
--- a/backend/src/app.ts
+++ b/backend/src/app.ts
@@ -4,7 +4,7 @@ import route from 'koa-route'
 import Debug from 'debug'
 import koaBody from 'koa-body'
 import func from './func'
-import { ErrorDescEnum, HttpError } from './types/HttpError'
+import { ErrorDescEnum, HttpError } from './classes/HttpError'
 import { PrismaClient } from '@prisma/client'
 
 dotenv.config()
@@ -73,6 +73,10 @@ app.use(route.post('/payer', async (ctx) => {
 	ctx.status = 204
 }))
 
+app.use(route.post('/invoice', async (ctx) => {
+
+}))
+
 const port = parseInt(process.env.PORT ?? '3000')
 app.listen(port, () => {
 	console.log(`Server is running at http://localhost:${port}`)
diff --git a/backend/src/types/HttpError.ts b/backend/src/classes/HttpError.ts
similarity index 74%
rename from backend/src/types/HttpError.ts
rename to backend/src/classes/HttpError.ts
index c709b30..e46b5a0 100644
--- a/backend/src/types/HttpError.ts
+++ b/backend/src/classes/HttpError.ts
@@ -48,7 +48,22 @@ enum ErrorDescEnum {
 	/**
 	 * 项目已存在。通常与 HTTP 状态码 400 Bad Request 一起使用。
 	 */
-	item_exists = 'item_exists'
+	item_exists = 'item_exists',
+
+	/**
+	 * 项目不存在。通常与 HTTP 状态码 404 Not Found 一起使用。
+	 */
+	item_not_found = 'item_not_found',
+
+	/**
+	 * 未授权。通常与 HTTP 状态码 401 Unauthorized 一起使用。
+	 */
+	unauthorized = 'unauthorized',
+
+	/**
+	 * 关联项目不存在。例如，创建新收据时，指定的付款人不存在。通常与 HTTP 状态码 400 Bad Request 一起使用。
+	 */
+	related_item_not_found = 'related_item_not_found'	
 }
 
 export { HttpError, ErrorDescEnum }
\ No newline at end of file
diff --git a/backend/src/classes/Invoice.ts b/backend/src/classes/Invoice.ts
new file mode 100644
index 0000000..f1725ae
--- /dev/null
+++ b/backend/src/classes/Invoice.ts
@@ -0,0 +1,196 @@
+import { PrismaClient } from "@prisma/client"
+import InvoiceItem from "./InvoiceItem"
+
+class Invoice {
+	/**
+	 * 创建新的收据实体
+	 */
+	constructor(invoiceId?: number, issueDate?: Date, newInvoiceInfo?: { period: Date[], items: InvoiceItem[], payerId: number, dueDate?: Date }) {
+		(async () => {
+			const prismaClient = new PrismaClient()
+
+			if (invoiceId && issueDate) {
+				// 从数据库查找收据
+				const invoice = await prismaClient.invoice.findUnique({
+					where: {
+						invoice_date_invoice_suffix_code: {
+							invoice_suffix_code: invoiceId % 1000,
+							invoice_date: new Date(invoiceId / 1000)
+						}
+					}
+				})
+				if (!invoice) throw new Error('invoice not found')
+
+				// 设置收据后缀
+				this.suffixCode = invoice.invoice_suffix_code
+
+				// 设置签发时间
+				this.issueTime = invoice.invoice_date
+
+				// 设置账单周期
+				this.period = [invoice.invoice_billing_period_start, invoice.invoice_billing_period_end]
+
+				// 设置项目列表
+				const items = await prismaClient.invoiceItem.findMany({
+					where: {
+						invoice_date: this.issueTime,
+						invoice_suffix_code: this.suffixCode
+					}
+				})
+				if (!items) this.items = []
+				else {
+					this.items = []
+					items.forEach((item) => {
+						this.items.push(new InvoiceItem(item.item_id, item.item_description, item.item_quantity, item.item_unit, item.item_unit_price))
+					})
+				}
+
+				// 设置收款日期
+				this.dueDate = invoice.invoice_due_date
+
+				// 设置付款人
+				this.payer = {
+					id: invoice.payer_id,
+					name: invoice.invoice_payer_name,
+					address: invoice.invoice_payer_address,
+					abn: invoice.invoice_payer_abn ? invoice.invoice_payer_abn : undefined,
+				}
+
+				// 设置备注
+				this.note = invoice.invoice_note ?? undefined
+			} else if (newInvoiceInfo) {
+				// 设置账单签发时间
+				this.issueTime = new Date()
+
+				// 设置账单周期
+				if (newInvoiceInfo.period.length !== 2) throw new Error('period should contain two dates')
+				this.period = newInvoiceInfo.period
+
+				// 设置项目列表
+				this.items = newInvoiceInfo.items
+
+				// 设置收款日期
+				this.dueDate = newInvoiceInfo.dueDate || new Date()
+
+				// 设置付款人
+				const payer = await prismaClient.payer.findUnique({
+					where: {
+						payer_id: newInvoiceInfo.payerId
+					}
+				})
+				if (!payer) throw new Error('payer not found')
+				this.payer = {
+					id: payer.payer_id,
+					name: payer.payer_name,
+					address: payer.payer_address,
+					abn: payer.payer_abn ? payer.payer_abn : undefined,
+					email: payer.payer_email
+				}
+
+				// 将收据保存到数据库
+				await prismaClient.invoice.create({
+					data: {
+						invoice_suffix_code: this.suffixCode,
+						invoice_date: this.issueTime,
+						invoice_billing_period_start: this.period[0],
+						invoice_billing_period_end: this.period[1],
+						invoice_due_date: this.dueDate,
+						payer_id: this.payer.id,
+						invoice_payer_address: this.payer.address,
+						invoice_payer_abn: this.payer.abn,
+						invoice_payer_name: this.payer.name,
+						invoice_total_amount: this.getTotal()
+					}
+				})
+
+				// 将项目保存到数据库
+				await Promise.all(this.items.map(async (item) => {
+					await prismaClient.invoiceItem.create({
+						data: {
+							invoice_suffix_code: this.suffixCode,
+							invoice_date: this.issueTime,
+							item_description: item.description ?? '',
+							item_quantity: item.quantity ?? 0,
+							item_unit: item.unit ?? '',
+							item_unit_price: item.unitPrice?.toNumber() ?? 0,
+							item_id: item.id
+						}
+					})
+				}))
+			}
+			prismaClient.$disconnect()
+		})()
+	}
+
+	/**
+	 * 收据后缀。仅在当日唯一。
+	 */
+	suffixCode!: number;
+
+	/**
+	 * 签发时间。与后缀一起构成发票的唯一标识。
+	 */
+	issueTime!: Date;
+
+	/**
+	 * 账单周期
+	 */
+	period!: Date[];
+
+	/**
+	 * 项目列表
+	 */
+	items!: InvoiceItem[];
+
+	/**
+	 * 收款日期
+	 */
+	dueDate!: Date;
+
+	/**
+	 * 付款人
+	 */
+	payer!: {
+		id: number;
+		name: string;
+		address: string;
+		abn?: string;
+		email?: string;
+	}
+
+	/**
+	 * 备注
+	 */
+	note?: string;
+
+	/**
+	 * 获取账单总额
+	 */
+	getTotal() {
+		let total = 0
+		this.items.forEach((item) => {
+			total += item.getSubtotal()
+		})
+		return total
+	}
+
+	/**
+	 * 更改备注
+	 * @param note 新的备注
+	 */
+	async setNote(note: string) {
+		this.note = note
+		const prismaClient = new PrismaClient()
+		await prismaClient.invoice.update({
+			where: {
+				invoice_date_invoice_suffix_code: {
+					invoice_suffix_code: this.suffixCode,
+					invoice_date: this.issueTime
+				}
+			},
+			data: {
+				invoice_note: note
+			}
+		})
+	}
+}
\ No newline at end of file
diff --git a/backend/src/classes/InvoiceItem.ts b/backend/src/classes/InvoiceItem.ts
new file mode 100644
index 0000000..33942ac
--- /dev/null
+++ b/backend/src/classes/InvoiceItem.ts
@@ -0,0 +1,54 @@
+import { Decimal } from 'decimal.js';
+
+class InvoiceItem {
+	/**
+	 * 创建一个新的收据项目实体。
+	 * @param id 收据项目的 ID。
+	 * @param description 项目的名称/描述。
+	 * @param quantity 项目的数量。
+	 * @param unit 项目的单位。
+	 * @param unitPrice 项目的单价。
+	 */
+	constructor(id: number, description: string, quantity: number, unit: string, unitPrice: Decimal) {
+		this.id = id
+		this.description = description
+		this.quantity = quantity
+		this.unit = unit
+		this.unitPrice = unitPrice
+	} 
+
+	/**
+	 * 收据项目的 ID。
+	 */
+	id: number
+
+	/**
+	 * 项目的名称/描述。
+	 */
+	description?: string
+
+	/**
+	 * 项目的数量。
+	 */
+	quantity?: number
+
+	/**
+	 * 项目的单位。
+	 */
+	unit?: string
+
+	/**
+	 * 项目的单价。
+	 */
+	unitPrice?: Decimal
+
+	/**
+	 * 获取项目的小计。
+	 */
+	getSubtotal() {
+		if (!this.quantity || !this.unitPrice) return 0
+		return this.quantity * this.unitPrice.toNumber()
+	}
+}
+
+export default InvoiceItem
\ No newline at end of file
diff --git a/backend/src/func/createPayer.ts b/backend/src/func/createPayer.ts
index dedf362..3d93ff7 100644
--- a/backend/src/func/createPayer.ts
+++ b/backend/src/func/createPayer.ts
@@ -1,6 +1,6 @@
 import Debug from 'debug'
-import { ErrorDescEnum, HttpError } from '../types/HttpError'
-import { PrismaClient, Prisma } from '@prisma/client'
+import { ErrorDescEnum, HttpError } from '../classes/HttpError'
+import { PrismaClient } from '@prisma/client'
 
 console.log = Debug('invoiceIssuer:func/createPayer.ts')
 
@@ -12,7 +12,7 @@ console.log = Debug('invoiceIssuer:func/createPayer.ts')
  * @param {string} email - 付款人的电子邮件地址
  * @param {string} abn - 付款人的澳大利亚商业号码
  */
-export default async (prisma: PrismaClient<Prisma.PrismaClientOptions, never>, name: string, address: string[], email: string, abn?: string) => {
+export default async (prisma: PrismaClient, name: string, address: string[], email: string, abn?: string) => {
 	// 验证 ABN 是否已存在
 	const existingPayer = await prisma.payer.findFirst({
 		where: {
diff --git a/backend/src/func/issueInvoice.ts b/backend/src/func/issueInvoice.ts
new file mode 100644
index 0000000..28ff20c
--- /dev/null
+++ b/backend/src/func/issueInvoice.ts
@@ -0,0 +1,17 @@
+import Debug from 'debug'
+import { ErrorDescEnum, HttpError } from '../classes/HttpError'
+import { PrismaClient, InvoiceItem } from '@prisma/client'
+
+console.log = Debug('invoiceIssuer:func/issueInvoice.ts')
+
+export default async (prisma: PrismaClient, payerId: number, period: Date[], items: InvoiceItem[]) => {
+	// 验证付款人是否存在
+	const payer = await prisma.payer.findUnique({
+		where: {
+			payer_id: payerId
+		}
+	})
+	if (!payer) throw new HttpError(ErrorDescEnum.related_item_not_found, 400, ['payer_id'])
+
+	// 创建新收据
+}
\ No newline at end of file