In a 5-degree-of-freedom human-seat suspension system, an improved adaptive fuzzy sliding-mode controller is developed for the simplified model, incorporating the dynamics model of the MRF (magnetorheological fluid) damper into the control framework. This controller successfully mitigates the "chatter" issue associated with sliding-mode control, and it achieves favorable control results for the semi-active seat suspension system by utilizing the output damping force of the MRF damper.