A 4×4 wheeled vehicle was taken as an example to study the key technology of dynamic vehicle height adjustment based on full-hydraulic-control hydro-pneumatic spring. It was pointed out that the dynamic pressure of the hydropneumatic was the key to the dynamic vehicle height adjustment. Through mathematical modeling and simulation analysis,it was concluded that spring specification,road grade and vehicle speed had impacts on dynamic pressure. The dynamic pressure in the spring was maximum when the excitation frequency was the eigenfrequency of the vehicle body. The model and calculation of the dynamic pressure was verified on real test. It is necessary to calculate the dynamic pressure according to the actual situation and decide whether to install the pressure booster so as to ensure the reliability of dynamic vehicle height adjustment before designing the hydraulic principle of the vehicle attitude adjustment system.