Body-scanning technology is the most up-to-date technology for achieving the body information. It helps to set up the database of body sizes and some research for very close type of garment. In this article we discuss a new method for describing the 3D shape of garment and set up its mathematic model for simulation, which is by dint of body scanning technology. Experiment was designed for investigating the changing for outside shape as the pattern parameters are changing. Samples were made and scanned by body scanning system, which they were put on the standard type of female model. The scanning point cloud files from Telmat scanning system were transferred into the Imageware software and the 3D scanning models were analyzed in important horizontal and vertical sections to discuss the shape changing. The 2-stage least Square is used to describe the outline of important sections. And the patch approaching is used to simulating complex free curved surface. The result helped to set up the 3D simulation model for woman warm jacket in our designing system. A new describing and simulating method for 3D garment model is discussed for research about garment CAD system. And it opens our mind to utilize body-scanning technology for deeper science research in many fields.