Abstract: Based on the background for layout design of simplified international commercial comsat cabin （INTELSAT-III）,several key techniques in the process of secondary development of Pro/Engineer are discussed.These include the choice of software’s edition and development mode,the interface customizing and procedure controlling of application,the definition and partition of layout subspace,the techniques of selforientation and assembly,the function outsourcing of Pro/Engineer and so on. These techniques of secondary development have been validated by the CAD system of layout,and are helpful to improve the research and application of Pro/Engineer secondary development.