Solution:
1. Right-click any blank space on the desktop, find "Personalization" and click Enter;
2. Find the "window color" below and click enter;
3. Check the "Enable Transparency Effect" below;
4. Click "Save Changes";
5. The taskbar/window border/start menu all become transparent;
The methods of setting transparent taskbar, window border and start menu in win7 system are shared here, and interested users can experience the settings.