Abstract: The typical obstacle-surmounting performances of wheel-track vehicle chassis were studied in this paper. At first, the sizes of variant wheel were designed according to a certain vehicle and the three dimensional models were established. Then the critical states of crossing trench, climbing step and slope were determined based on kinematics and mechanical analysis, and the largest width across trench, the height over the step and the maximum slope angle were obtained respectively. The results show that the wheel-track vehicle chassis has stronger environmental adaptability and higher obstacle-surmounting performance than the normal wheel vehicle and track vehicle. These achievements provide a sufficient theoretical basis for optimum of structure and the extend application of the wheel-track vehicle in the future.