To improve the safety and stability of the wheeled off-road vehicles, the impact of the key element balance valve in the drive system on the performance of the off-road vehicles hydraulic driving system is studied. The hydraulic driving system of the off-road vehicle is taken as an example to establish the theoretical analysis model of the balance valve. By means of establishing the hydraulic drive system model of the off-road vehicle through AMESim software, the pressure and speed of the pump，hydraulic motor, and balance valve in the drive system under flat road driving conditions and downhill driving conditions are analyzed. The correctness of the simulation model is verified through experiments. The results indicate that the balance valve has the functions of balancing negative loads, preventing insufficient fuel supply and hydraulic motor stalls under downhill conditions. In order to improve the shock in the downhill process, damping groove depth and orifice diameter at the control end of the balance valve spool are optimized. Through the analysis results, it is found that changing the damping groove depth can effectively reduce the pressure shock, and when the groove depth is reduced from 0.55 mm to 0.35 mm, the back pressure can be reduced by 12.5%. The theoretical model and simulation model provides a reliable basis for the further optimization of the hydraulic driving system of the off-road vehicle.