As a common design type and visual art form, collage is widely used in poster design, logo production, and other applications. However, traditional manual process requires a lot of repetitive attempts and it is difficult for designers to achieve the optimal layout. When using computers to solve problems, there are many different ways. This paper summarizes different collage ideas which are roughly concluded as two ideas of top-down and bottom-up, and their algorithm routes are analyzed and compared. Finally, future development trend of the problem is presented.