diff --git a/Assets/YooAsset/Editor/AssetBundleBrowser/AssetBundleBrowserWindow.cs b/Assets/YooAsset/Editor/AssetBundleBrowser/AssetBundleBrowserWindow.cs
index b54eefe..f2f7637 100644
--- a/Assets/YooAsset/Editor/AssetBundleBrowser/AssetBundleBrowserWindow.cs
+++ b/Assets/YooAsset/Editor/AssetBundleBrowser/AssetBundleBrowserWindow.cs
@@ -1,3 +1,4 @@
+#if UNITY_2019_4_OR_NEWER
 using System.IO;
 using System.Linq;
 using System.Collections.Generic;
@@ -114,4 +115,5 @@ namespace YooAsset.Editor
 			}
 		}
 	}
-}
\ No newline at end of file
+}
+#endif
\ No newline at end of file
diff --git a/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/AssetListViewer.cs b/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/AssetListViewer.cs
index 4ee158f..128cbfb 100644
--- a/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/AssetListViewer.cs
+++ b/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/AssetListViewer.cs
@@ -1,3 +1,4 @@
+#if UNITY_2019_4_OR_NEWER
 using System.IO;
 using System.Linq;
 using System.Collections.Generic;
@@ -238,4 +239,5 @@ namespace YooAsset.Editor
 				return (EditorTools.GetFileSize(fullPath) / 1024f).ToString("f1") + " KB";
 		}
 	}
-}
\ No newline at end of file
+}
+#endif
\ No newline at end of file
diff --git a/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/BundleListViewer.cs b/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/BundleListViewer.cs
index 11ba5dc..d27b4e6 100644
--- a/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/BundleListViewer.cs
+++ b/Assets/YooAsset/Editor/AssetBundleBrowser/VisualViewers/BundleListViewer.cs
@@ -1,3 +1,4 @@
+#if UNITY_2019_4_OR_NEWER
 using System.IO;
 using System.Linq;
 using System.Collections.Generic;
@@ -291,4 +292,5 @@ namespace YooAsset.Editor
 			return result;
 		}
 	}
-}
\ No newline at end of file
+}
+#endif
\ No newline at end of file