diff --git a/backend/packages/harness/deerflow/sandbox/local/local_sandbox.py b/backend/packages/harness/deerflow/sandbox/local/local_sandbox.py
index eaf1ed0ad..ebadbf7b8 100644
--- a/backend/packages/harness/deerflow/sandbox/local/local_sandbox.py
+++ b/backend/packages/harness/deerflow/sandbox/local/local_sandbox.py
@@ -376,7 +376,9 @@ class LocalSandbox(Sandbox):
 
         def replace_match(match: re.Match) -> str:
             matched_path = match.group(0)
-            return self._resolve_path(matched_path)
+            # Normalize to forward slashes so bash doesn't interpret Windows
+            # backslash sequences (\\U, \\a, \\d, \\s, \\n, \\t) as escapes.
+            return self._resolve_path(matched_path).replace("\\", "/")
 
         return pattern.sub(replace_match, command)
 
diff --git a/backend/packages/harness/deerflow/sandbox/tools.py b/backend/packages/harness/deerflow/sandbox/tools.py
index 1440bb8e3..5217d80d7 100644
--- a/backend/packages/harness/deerflow/sandbox/tools.py
+++ b/backend/packages/harness/deerflow/sandbox/tools.py
@@ -1049,7 +1049,7 @@ def replace_virtual_paths_in_command(command: str, thread_data: ThreadDataState
         skills_pattern = re.compile(rf"{re.escape(skills_container)}(/[^\s\"';&|<>()]*)?")
 
         def replace_skills_match(match: re.Match) -> str:
-            return _resolve_skills_path(match.group(0))
+            return _resolve_skills_path(match.group(0)).replace("\\", "/")
 
         result = skills_pattern.sub(replace_skills_match, result)
 
@@ -1060,7 +1060,7 @@ def replace_virtual_paths_in_command(command: str, thread_data: ThreadDataState
         acp_pattern = re.compile(rf"{re.escape(_ACP_WORKSPACE_VIRTUAL_PATH)}(/[^\s\"';&|<>()]*)?")
 
         def replace_acp_match(match: re.Match, _tid: str | None = _thread_id) -> str:
-            return _resolve_acp_workspace_path(match.group(0), _tid)
+            return _resolve_acp_workspace_path(match.group(0), _tid).replace("\\", "/")
 
         result = acp_pattern.sub(replace_acp_match, result)
 
@@ -1071,7 +1071,7 @@ def replace_virtual_paths_in_command(command: str, thread_data: ThreadDataState
         pattern = re.compile(rf"{re.escape(VIRTUAL_PATH_PREFIX)}(/[^\s\"';&|<>()]*)?")
 
         def replace_user_data_match(match: re.Match) -> str:
-            return replace_virtual_path(match.group(0), thread_data)
+            return replace_virtual_path(match.group(0), thread_data).replace("\\", "/")
 
         result = pattern.sub(replace_user_data_match, result)
 
diff --git a/backend/tests/test_sandbox_windows_path_normalization.py b/backend/tests/test_sandbox_windows_path_normalization.py
new file mode 100644
index 000000000..211537cd6
--- /dev/null
+++ b/backend/tests/test_sandbox_windows_path_normalization.py
@@ -0,0 +1,79 @@
+"""Regression tests for Windows backslash path normalization.
+
+Ensures that replace_virtual_paths_in_command and LocalSandbox._resolve_paths_in_command
+return forward-slash paths when the host paths use backslashes (Windows).
+"""
+
+from unittest.mock import patch
+
+from deerflow.sandbox.local.local_sandbox import LocalSandbox, PathMapping
+from deerflow.sandbox.tools import replace_virtual_paths_in_command
+
+# Windows-style thread data with backslash paths
+_WIN_THREAD_DATA = {
+    "workspace_path": r"C:\Users\admin\deer-flow\backend\.deer-flow\users\user1\threads\t1\user-data\workspace",
+    "uploads_path": r"C:\Users\admin\deer-flow\backend\.deer-flow\users\user1\threads\t1\user-data\uploads",
+    "outputs_path": r"C:\Users\admin\deer-flow\backend\.deer-flow\users\user1\threads\t1\user-data\outputs",
+}
+
+
+class TestReplaceVirtualPathsWindows:
+    """replace_virtual_paths_in_command must normalize backslashes to forward slashes."""
+
+    def test_user_data_workspace_no_backslash(self) -> None:
+        cmd = "cat /mnt/user-data/workspace/data.json"
+        result = replace_virtual_paths_in_command(cmd, _WIN_THREAD_DATA)
+        assert "\\" not in result, f"Backslash in: {result}"
+
+    def test_user_data_outputs_no_backslash(self) -> None:
+        cmd = "ls /mnt/user-data/outputs/report.html"
+        result = replace_virtual_paths_in_command(cmd, _WIN_THREAD_DATA)
+        assert "\\" not in result, f"Backslash in: {result}"
+
+    def test_user_data_subdir_no_backslash(self) -> None:
+        cmd = "cat /mnt/user-data/workspace/subdir/file.txt"
+        result = replace_virtual_paths_in_command(cmd, _WIN_THREAD_DATA)
+        assert "\\" not in result, f"Backslash in: {result}"
+
+    @patch("deerflow.sandbox.tools._get_skills_host_path", return_value=r"C:\Users\admin\deer-flow\skills")
+    @patch("deerflow.sandbox.tools._get_skills_container_path", return_value="/mnt/skills")
+    def test_skills_path_no_backslash(self, _mock_container, _mock_host) -> None:
+        cmd = "python /mnt/skills/custom/skill/scripts/run.py"
+        result = replace_virtual_paths_in_command(cmd, _WIN_THREAD_DATA)
+        assert "\\" not in result, f"Backslash in: {result}"
+
+    @patch("deerflow.sandbox.tools._resolve_acp_workspace_path", return_value=r"C:\Users\admin\deer-flow\acp-workspace\data.json")
+    @patch("deerflow.sandbox.tools._get_acp_workspace_host_path", return_value=r"C:\Users\admin\deer-flow\acp-workspace")
+    def test_acp_workspace_no_backslash(self, _mock_acp_host, _mock_resolve_acp) -> None:
+        cmd = "cat /mnt/acp-workspace/data.json"
+        result = replace_virtual_paths_in_command(cmd, _WIN_THREAD_DATA)
+        assert "\\" not in result, f"Backslash in: {result}"
+        assert "C:/Users/admin/deer-flow/acp-workspace/data.json" in result
+
+
+class TestLocalSandboxResolvePathsInCommandWindows:
+    """LocalSandbox._resolve_paths_in_command must normalize backslashes."""
+
+    def test_custom_mount_no_backslash(self) -> None:
+        sandbox = LocalSandbox(
+            "test",
+            path_mappings=[
+                PathMapping(container_path="/mnt/models", local_path=r"C:\Users\admin\models", read_only=True),
+            ],
+        )
+        cmd = "cat /mnt/models/weights.bin"
+        result = sandbox._resolve_paths_in_command(cmd)
+        assert "\\" not in result, f"Backslash in: {result}"
+        assert "C:/Users/admin/models/weights.bin" in result
+
+    def test_user_data_no_backslash(self) -> None:
+        sandbox = LocalSandbox(
+            "test",
+            path_mappings=[
+                PathMapping(container_path="/mnt/user-data", local_path=r"C:\Users\admin\data"),
+            ],
+        )
+        cmd = "ls /mnt/user-data/workspace/file.txt"
+        result = sandbox._resolve_paths_in_command(cmd)
+        assert "\\" not in result, f"Backslash in: {result}"
+        assert "C:/Users/admin/data/workspace/file.txt" in result