diff --git a/src/fs/common.test.ts b/src/fs/common.test.ts
new file mode 100644
index 0000000..23469b5
--- /dev/null
+++ b/src/fs/common.test.ts
@@ -0,0 +1,79 @@
+import assert from 'node:assert/strict'
+// eslint-disable-next-line test/no-import-node-test
+import { describe, it } from 'node:test'
+
+/**
+ * 模拟 forceUpdateContent 中的解码逻辑
+ * 原代码: new TextDecoder().decode(content) — 默认 UTF-8，GB2312 会乱码
+ * 修复后: 先 UTF-8，检测到大量替换字符时 fallback 到 GBK
+ */
+function decodeFileContent(content: Uint8Array): string {
+  // 先尝试 UTF-8 严格解码
+  try {
+    return new TextDecoder('utf-8', { fatal: true }).decode(content)
+  }
+  catch {
+    // UTF-8 解码失败（包含非法字节序列），尝试 GBK/GB2312
+    try {
+      return new TextDecoder('gbk').decode(content)
+    }
+    catch {
+      // GBK 也不可用时，回退到宽松 UTF-8
+      return new TextDecoder('utf-8', { fatal: false }).decode(content)
+    }
+  }
+}
+
+describe('GB2312/GBK encoding handling', () => {
+  it('decodes UTF-8 content correctly', () => {
+    const text = 'Hello世界Test测试'
+    const utf8Bytes = new TextEncoder().encode(text)
+    const result = decodeFileContent(utf8Bytes)
+    assert.equal(result, text)
+  })
+
+  it('falls back to GBK when UTF-8 produces replacement characters', () => {
+    // "你好" in GBK/GB2312: C4 E3 BA C3
+    const gbkBytes = new Uint8Array([0xC4, 0xE3, 0xBA, 0xC3])
+    const result = decodeFileContent(gbkBytes)
+    assert.equal(result, '你好', `Expected "你好", got "${result}"`)
+  })
+
+  it('handles ASCII-only content without fallback', () => {
+    const text = 'Hello World 123'
+    const bytes = new TextEncoder().encode(text)
+    const result = decodeFileContent(bytes)
+    assert.equal(result, text)
+  })
+
+  it('handles mixed Chinese GBK content', () => {
+    // "中文GBK测试" in GBK
+    // 中 = D6 D0, 文 = CE C4, G=47, B=42, K=4B, 测 = B2 E2, 试 = CA D4
+    const gbkMixed = new Uint8Array([
+      0xD6, 0xD0, // 中
+      0xCE, 0xC4, // 文
+      0x47, 0x42, 0x4B, // GBK (ASCII)
+      0xB2, 0xE2, // 测
+      0xCA, 0xD4, // 试
+    ])
+    const result = decodeFileContent(gbkMixed)
+    assert.equal(result, '中文GBK测试', `Expected "中文GBK测试", got "${result}"`)
+  })
+
+  it('falls back to GBK for pure GBK content (not mixed UTF-8+broken bytes)', () => {
+    // 真实场景：一个纯 GBK 编码的文本文件
+    // "中文内容测试" 的 GBK 编码
+    const gbkContent = new Uint8Array([
+      0xD6, 0xD0, 0xCE, 0xC4, // 中文
+      0xC4, 0xDA, 0xC8, 0xDD, // 内容
+      0xB2, 0xE2, 0xCA, 0xD4, // 测试
+    ])
+    const result = decodeFileContent(gbkContent)
+    assert.equal(result, '中文内容测试', `Expected "中文内容测试", got "${result}"`)
+  })
+
+  it('handles empty content', () => {
+    const result = decodeFileContent(new Uint8Array(0))
+    assert.equal(result, '')
+  })
+})
diff --git a/src/fs/common.ts b/src/fs/common.ts
index 9482154..3abab45 100644
--- a/src/fs/common.ts
+++ b/src/fs/common.ts
@@ -120,8 +120,29 @@ function createSequentialFunction<T extends (...args: any[]) => Promise<any>>(fn
   return ((...args) => lastPromise = lastPromise.then(() => fn(...args))) as T
 }
 
+/**
+ * 解码文件内容，自动处理 GB2312/GBK 编码。
+ * 先用 UTF-8 严格解码，失败时 fallback 到 GBK。
+ */
+export function decodeTextFileContent(content: Uint8Array): string {
+  try {
+    // 先尝试 UTF-8 严格解码 — 纯 ASCII 和 UTF-8 都能通过
+    return new TextDecoder('utf-8', { fatal: true }).decode(content)
+  }
+  catch {
+    // UTF-8 解码失败（包含非法字节序列），尝试 GBK/GB2312
+    try {
+      return new TextDecoder('gbk').decode(content)
+    }
+    catch {
+      // GBK 也不可用时，回退到宽松 UTF-8（可能乱码，但不会崩溃）
+      return new TextDecoder('utf-8', { fatal: false }).decode(content)
+    }
+  }
+}
+
 export function forceUpdateContent(uri: Uri | string, doc: Y.Doc, content: Uint8Array) {
-  const newText = new TextDecoder().decode(content)
+  const newText = decodeTextFileContent(content)
   const oldText = doc.getText().toString()
   if (oldText !== newText) {
     doc.transact(() => {
diff --git a/src/fs/host.ts b/src/fs/host.ts
index 325fb7d..9f40c88 100644
--- a/src/fs/host.ts
+++ b/src/fs/host.ts
@@ -6,7 +6,7 @@ import picomatch from 'picomatch'
 import { useDisposable } from 'reactive-vscode'
 import { Disposable, FileChangeType, RelativePattern, Uri, workspace } from 'vscode'
 import * as Y from 'yjs'
-import { forceUpdateContent, fsErrorWrapper, setupTextDocumentUpdater, useTextDocumentWatcher } from './common'
+import { decodeTextFileContent, forceUpdateContent, fsErrorWrapper, setupTextDocumentUpdater, useTextDocumentWatcher } from './common'
 
 export function useHostFs(connection: Connection) {
   const { toHostUri, toTrackUri } = connection
@@ -46,7 +46,7 @@ export function useHostFs(connection: Connection) {
       const uri_ = toHostUri(Uri.parse(uri))
       setupTextDocumentUpdater(uri_, doc)
 
-      const newText = content ?? new TextDecoder().decode(await workspace.fs.readFile(uri_))
+      const newText = content ?? decodeTextFileContent(new Uint8Array(await workspace.fs.readFile(uri_)))
       doc.getText().insert(0, newText)
 
       return Y.encodeStateAsUpdateV2(doc)