The Twin-rotor piston engine (TRPE) is a new type of differential rotary engine. In the paper, the working characteristics of the TRPE are analyzed, and the mechanical structure characteristics of the TRPE differential velocity mechanism (DVM) are figured out. After defining the DVM dynamic parameters, the mathematical models of the kineto-static analysis for the DVM are established by using the vector mechanics methods. The mathematical models are calculated by Matlab soft programming, and the mechanical characteristics of DVM main components are obtained.