In order to study the dynamic shift characteristics of the transmission control system of the SD-5 crawler hydraulic bulldozer, based on the analysis of the structure and working principle of the transmission valve and clutch, a mechanicalhydraulic cosimulation model of the transmission control system was built by using SimulationX software. The dynamic shift characteristics of the transmission control system under different operating conditions were analyzed, and the influences of spring stiffness, orifice and quickreturn valve structural parameters on the shift characteristics were analyzed.The results show that the forward gear of the transmission control system has better shift characteristics, while the reverse gear has more serious pressure shock; the greater the clutch spring stiffness is, the smaller the pressure shock is; the orifice R1 is the main factor affecting the pressure regulating time; the pressure shock of the reverse shift can be effectively improved by setting the orifice R2; the pressure shock phenomenon can be effectively improved by optimizing the structural parameters of the fastreturn valve. The research results provide a reference for the performance optimization and energy saving research of the bulldozer transmission system.