A disturbance observer was proposed to estimate and to compensate the load disturbance of the variable frequency pump-control-motor speed governing system. In order to improve the robustness and performance of the system, a sliding mode variable structure controller was designed to weaken the impact on the system of the disturbance. The proof on robustness of the system was conducted. Simulation results verified that the designed controller shows good robustness to the load disturbance and system parameters uncertainty, which effectively improves the precision of speed control and meets the requirements of the pump-control-motor speed governing system. 