The method to satisfied the high requirement of aviation to aero assembly time and quality is setting up movable type production line. Combine Q400 joining mobile production line,we make an in-depth study to work principle and distinguishing feature of air cushion floating device. In this article description and design of mobile jig structure is stressed, and finite element analysis and detailed calculation or analysis to the main technical parameters of cushion device as:layout,quantity,driving force and so on is also included in. The application of cushion suspension device to mobile type production line satisfy the aeroplane assembly requirement of high quality and high efficiency. Research results could be used as reference for other aerocraft mobile production line.