Abstract: In order to carry out a reliable control for a semi-active suspension system of an engineering vehicle, a mathematic model of single chamber hydro-pneumatic spring was established. The characteristics of spring rate and damping rate as well as the relationship between throttle area and damping force were analyzed. The control strategy of improving vehicle ride comfort without the frequent suspension breakdown was proposed. The fuzzy logic control (FLC) model with the inputs of suspension deflection and its change rate with time was established. The rules of fuzzy logic control were worked out and the fuzzy logic controller was designed. The responses were simulated under the conditions of road surfaces with sine, integrated random white noise and instant step input excitation, respectively. According to simulation results, the application of FLC in semi-active suspension controlling not only reduces the frequency of suspension breakdown, but also improves the ride performance from statistic point of view.