Motion differential equation of hydro-pneumatic suspension is established to describe the vibration characteristics for a certain type of construction vehicles. The output force was deduced from the suspension parameters. Based on the suspension characteristics of multi-phase medium, fractional calculus theory was introduced, and its fractional Bagley-Torvik equation was set up. The numerical computation by low-pass filter of Oustaloup algorithm was performed. The numerical solution of nonlinear fractional equation was obtained to investigate the vibration characteristics of the suspension fractional system. By the build of equal-ratio test platform and simulation model, the fractional, integer order model simulation and experimental data were compared. When the fractional-order is 0.9, it better describes the motion characteristics of suspension system. The experiments show that the experimental data can fit the fractional order system model well, thereby prove the model on hydro pneumatic suspension system.