With the basic function of CAD software system it's convenient to realize information analysis and pick up of built-in geometrical elements, but it's difficult to non built-in geometrical elements, it is intended to discuss how to build software system under HOOPS/ACIS platform, and how to deal with the problem of CAD's file model process, explainhow to decide the module processing system. And in details, achieve the function of main module, and the way of technical implementation.