Hi liubo934006704
You will need to increase the Antialiasing setting in the Trainz Settings. You can do this by following these steps:
1) Double click on the Trainz icon on your desktop
2) Click on Trainz Settings
3) Click on the Performance tab
4) Set the 'antialiasing' setting to 8x
Please note, increasing this setting will impact on performance. However the higher antialiasing settings are required to produce better looking transparency, such as for windows or lights.