Aiming at the necessity of cutoff valve in vehicle altitude adjusting system of a wheel vehicle, the mathematical model of oil and gas spring-cutoff valvehydraulic line-hydraulic lock and the simulation model were established, mainly analyzing the pressure pulsation in the pipeline under different velocity of the piston rod. The simulation results show that the instantaneous velocity of the piston rod will produce instantaneous hydraulic impact and cause severe pressure pulsation in the hydraulic pipeline, the pressure fluctuation peak will affect the performance of the oil-gas spring and cause hose bursting damage. So it is necessary to keep the cut-off valve.