In order to reduce vibrations in a heavy truck cab, a lumped mass model is built to find an efficient control method for the semi-active cab mounting system based on a magnetorheological damper. The controller is designed using PID control theory and the fuzzy optimum control method. The parameters of the fuzzy optimum controller are optimized by using the dynamic characteristics experimental data of the magnetorheological damper. By taking the acceleration magnitude of the cab centroid's vertical, roll and pitch as the control objectives, the numerical simulation is carried out with ADAMS/Simulink software, and two control strategies are applied and compared. Experiments with a real truck experiencing road excitation are performed. The simulated and experimental results show that the PID and fuzzy optimum control can reduce the vibration of the cab compared with the passive status, and the fuzzy optimum control method is more effective.