With the development of information technology, the traditional software development methods cannot adapt to the requirement of users. In order to use the minimum resources to gain the maximum market share, a large number of software development companies need a flexible architecture to extend software functions based on a set of codes. This paper compares the current software extension methods, analyzes their advantages and disadvantages, and proposes a new software extension method—plug-in development method. It gives the definition and usage of plug-in development method. At the same time, the advantages and disadvantages of this method are analyzed, and the proposed usage scene is put forward.