Effective secondary development is the key process for CAD application. But as a cross-disciplinary problem and new software development mode, secondary development based on commercial CAD software has new features compared with complete independent software development. From angle of software engineering, this paper summarizes demand of software engineering, standards to observe, software development flow, configuration of development team in the process of commercial CAD software secondary development. Finally, this paper presents the case of secondary development of AutoCAD standard base parametric system to illustrate the specific application of software engineering in detail.