Abstract: In order to enhance performances for an engineering vehicle, mathematic models of its single chamber hydro-pneumatic spring were established to analyze the effects of stiffness and damping as well as friction on suspension dynamics. A fuzzy PID (F-PID) control model was established with vehicular suspension dynamic deflection as the control input. The fuzzy logic control rules were settled and a semi-active suspension F-PID controller was designed with Matlab/Simulink programming. The responses under instant excitation road input were simulated respectively. According to simulation results, the application of F-PID in semi-active suspension controlling not only improves vehicular ride performance, but also makes the responses rapidly and stably as well as decreases the oscillation. Research conclusions may provide some of references for studying the semi-active control of vehicle suspension.