Abstract: Under UNIX environment and on MSC/Patran platform, a pre-and post-processor of structural optimization system is developed. The work is done with adding special commands and windows using the development tool PCL provided by Patran for the customization of MSC/Patran. The available modules of numerical computation are integrated and the engineering program system is finally formed. The pre-and post-processor of the system developed by above technique can keep the original powerful functions of the platform. Besides attracting users, it is easy to be developed. The practicability and efficiency of the system are showed with examples.