A nonlinear mathematical model of the gas oil mixed hydro-pneumatic suspension used on mining dump trucks was presented. The gas dissolution effect, as well as the oil compressibility was taken into account in the model. The effects of gas dissolution and oil compressibility on the pressure changes within the hydro-pneumatic suspension were analyzed by solving the nonlinear mathematical equations. And the simulation results were compared with the experimental results. The results showed that the proposed model could describe the output force and pressure change of hydro-pneumatic suspension more accurately, and the effects of gas dissolution and oil compressibility couldn’t be ignored in hydro-pneumatic suspension research and design. Meanwhile, the effects were greater in compression stroke than expansion stroke. 