diff --git a/packages/playground/assets/__tests__/assets.spec.ts b/packages/playground/assets/__tests__/assets.spec.ts
index c671e93cbb308b..1b38346e49c700 100644
--- a/packages/playground/assets/__tests__/assets.spec.ts
+++ b/packages/playground/assets/__tests__/assets.spec.ts
@@ -6,7 +6,9 @@ import {
   isBuild,
   listAssets,
   readManifest,
-  readFile
+  readFile,
+  editFile,
+  notifyRebuildComplete
 } from '../../testUtils'
 
 const assetMatch = isBuild
@@ -195,3 +197,15 @@ if (isBuild) {
     }
   })
 }
+describe('css and assets in css in build watch', () => {
+  if (isBuild) {
+    test('css will not be lost and css does not contain undefined', async () => {
+      editFile('index.html', (code) => code.replace('Assets', 'assets'), true)
+      await notifyRebuildComplete(watcher)
+      const cssFile = findAssetFile(/index\.\w+\.css$/, 'foo')
+      expect(cssFile).not.toBe('')
+      expect(cssFile).not.toMatch(/undefined/)
+      watcher?.close()
+    })
+  }
+})
diff --git a/packages/playground/assets/vite.config.js b/packages/playground/assets/vite.config.js
index 113191c246a4a8..1ecd3318627521 100644
--- a/packages/playground/assets/vite.config.js
+++ b/packages/playground/assets/vite.config.js
@@ -13,6 +13,7 @@ module.exports = {
   },
   build: {
     outDir: 'dist/foo',
-    manifest: true
+    manifest: true,
+    watch: {}
   }
 }
diff --git a/packages/playground/testEnv.d.ts b/packages/playground/testEnv.d.ts
index a0633e43826b62..73fa5e62c73011 100644
--- a/packages/playground/testEnv.d.ts
+++ b/packages/playground/testEnv.d.ts
@@ -1,4 +1,5 @@
 import { Page } from 'playwright-chromium'
+import { RollupWatcher } from 'rollup'
 
 declare global {
   // injected by the custom jest env in scripts/jestEnv.js
@@ -7,4 +8,5 @@ declare global {
   // injected in scripts/jestPerTestSetup.ts
   const browserLogs: string[]
   const viteTestUrl: string
+  const watcher: RollupWatcher
 }
diff --git a/packages/playground/testUtils.ts b/packages/playground/testUtils.ts
index 3546b18c72aa45..9c7235e000c48f 100644
--- a/packages/playground/testUtils.ts
+++ b/packages/playground/testUtils.ts
@@ -66,8 +66,12 @@ export function readFile(filename: string) {
   return fs.readFileSync(path.resolve(testDir, filename), 'utf-8')
 }
 
-export function editFile(filename: string, replacer: (str: string) => string) {
-  if (isBuild) return
+export function editFile(
+  filename: string,
+  replacer: (str: string) => string,
+  runInBuild: boolean = false
+): void {
+  if (isBuild && !runInBuild) return
   filename = path.resolve(testDir, filename)
   const content = fs.readFileSync(filename, 'utf-8')
   const modified = replacer(content)
@@ -122,3 +126,8 @@ export async function untilUpdated(
     }
   }
 }
+
+/**
+ * Send the rebuild complete message in build watch
+ */
+export { notifyRebuildComplete } from '../../scripts/jestPerTestSetup'
diff --git a/packages/vite/src/node/plugins/asset.ts b/packages/vite/src/node/plugins/asset.ts
index 5b728d18dd6a01..dce0a8243c7aed 100644
--- a/packages/vite/src/node/plugins/asset.ts
+++ b/packages/vite/src/node/plugins/asset.ts
@@ -27,17 +27,21 @@ const assetHashToFilenameMap = new WeakMap<
   ResolvedConfig,
   Map<string, string>
 >()
+// save hashes of the files that has been emitted in build watch
+const emittedHashMap = new WeakMap<ResolvedConfig, Set<string>>()
 
 /**
  * Also supports loading plain strings with import text from './foo.txt?raw'
  */
 export function assetPlugin(config: ResolvedConfig): Plugin {
+  // assetHashToFilenameMap initialization in buildStart causes getAssetFilename to return undefined
+  assetHashToFilenameMap.set(config, new Map())
   return {
     name: 'vite:asset',
 
     buildStart() {
       assetCache.set(config, new Map())
-      assetHashToFilenameMap.set(config, new Map())
+      emittedHashMap.set(config, new Set())
     },
 
     resolveId(id) {
@@ -202,8 +206,6 @@ async function fileToBuiltUrl(
   }
 
   const file = cleanUrl(id)
-  const { search, hash } = parseUrl(id)
-  const postfix = (search || '') + (hash || '')
   const content = await fsp.readFile(file)
 
   let url
@@ -223,21 +225,26 @@ async function fileToBuiltUrl(
     // https://bundlers.tooling.report/hashing/asset-cascade/
     // https://github.com/rollup/rollup/issues/3415
     const map = assetHashToFilenameMap.get(config)!
-
     const contentHash = getAssetHash(content)
+    const { search, hash } = parseUrl(id)
+    const postfix = (search || '') + (hash || '')
+    const basename = path.basename(file)
+    const ext = path.extname(basename)
+    const fileName = path.posix.join(
+      config.build.assetsDir,
+      `${basename.slice(0, -ext.length)}.${contentHash}${ext}`
+    )
     if (!map.has(contentHash)) {
-      const basename = path.basename(file)
-      const ext = path.extname(basename)
-      const fileName = path.posix.join(
-        config.build.assetsDir,
-        `${basename.slice(0, -ext.length)}.${contentHash}${ext}`
-      )
       map.set(contentHash, fileName)
+    }
+    const emittedSet = emittedHashMap.get(config)!
+    if (!emittedSet.has(contentHash)) {
       pluginContext.emitFile({
         fileName,
         type: 'asset',
         source: content
       })
+      emittedSet.add(contentHash)
     }
 
     url = `__VITE_ASSET__${contentHash}__${postfix ? `$_${postfix}__` : ``}`
diff --git a/packages/vite/src/node/plugins/css.ts b/packages/vite/src/node/plugins/css.ts
index de27f4d845426b..c848931f2b3dd3 100644
--- a/packages/vite/src/node/plugins/css.ts
+++ b/packages/vite/src/node/plugins/css.ts
@@ -223,7 +223,8 @@ export function cssPlugin(config: ResolvedConfig): Plugin {
  * Plugin applied after user plugins
  */
 export function cssPostPlugin(config: ResolvedConfig): Plugin {
-  let styles: Map<string, string>
+  // styles initialization in buildStart causes a styling loss in watch
+  const styles: Map<string, string> = new Map<string, string>()
   let pureCssChunks: Set<string>
 
   // when there are multiple rollup outputs and extracting CSS, only emit once,
@@ -236,7 +237,6 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
 
     buildStart() {
       // Ensure new caches for every build (i.e. rebuilding in watch mode)
-      styles = new Map<string, string>()
       pureCssChunks = new Set<string>()
       outputToExtractedCSSMap = new Map<NormalizedOutputOptions, string>()
     },
diff --git a/scripts/jestPerTestSetup.ts b/scripts/jestPerTestSetup.ts
index f240ac430e056d..d578124341b7ad 100644
--- a/scripts/jestPerTestSetup.ts
+++ b/scripts/jestPerTestSetup.ts
@@ -2,8 +2,17 @@ import fs from 'fs-extra'
 import * as http from 'http'
 import { resolve, dirname } from 'path'
 import sirv from 'sirv'
-import { createServer, build, ViteDevServer, UserConfig } from 'vite'
+import {
+  createServer,
+  build,
+  ViteDevServer,
+  UserConfig,
+  PluginOption,
+  ResolvedConfig
+} from 'vite'
 import { Page } from 'playwright-chromium'
+// eslint-disable-next-line node/no-extraneous-import
+import { RollupWatcher, RollupWatcherEvent } from 'rollup'
 
 const isBuildTest = !!process.env.VITE_TEST_BUILD
 
@@ -18,6 +27,7 @@ declare global {
     interface Global {
       page?: Page
       viteTestUrl?: string
+      watcher?: RollupWatcher
     }
   }
 }
@@ -99,7 +109,22 @@ beforeAll(async () => {
         await page.goto(url)
       } else {
         process.env.VITE_INLINE = 'inline-build'
-        await build(options)
+        // determine build watch
+        let resolvedConfig: ResolvedConfig
+        const resolvedPlugin: () => PluginOption = () => ({
+          name: 'vite-plugin-watcher',
+          configResolved(config) {
+            resolvedConfig = config
+          }
+        })
+        options.plugins = [resolvedPlugin()]
+        const rollupOutput = await build(options)
+        const isWatch = !!resolvedConfig!.build.watch
+        // in build watch,call startStaticServer after the build is complete
+        if (isWatch) {
+          global.watcher = rollupOutput as RollupWatcher
+          await notifyRebuildComplete(global.watcher)
+        }
         const url = (global.viteTestUrl = await startStaticServer())
         await page.goto(url)
       }
@@ -168,3 +193,21 @@ function startStaticServer(): Promise<string> {
     })
   })
 }
+
+/**
+ * Send the rebuild complete message in build watch
+ */
+export async function notifyRebuildComplete(
+  watcher: RollupWatcher
+): Promise<RollupWatcher> {
+  let callback: (event: RollupWatcherEvent) => void
+  await new Promise((resolve, reject) => {
+    callback = (event) => {
+      if (event.code === 'END') {
+        resolve(true)
+      }
+    }
+    watcher.on('event', callback)
+  })
+  return watcher.removeListener('event', callback)
+}