Pump controlled hydraulic actuators are wildly used in the aerospace industry owing to the advantages of energy-saving and integrated configurations.Negative loads may occur to actuators due to external force loads or the inertial force when the actuator decelerates significantly.Uncertain negative load working conditions may cause cavitation,actuator vibration,and even instability to the motion control if the actuator is without sufficient meter-out damping.Various types of hydraulic configuration schemes have been proposed to deal with negative loads of hydraulic actuators.However,few of them can simultaneously achieve energy saving and high control accuracy.This study proposes an energy-saving and accurate motion tracking strategy for a hydraulic actuator with uncertain negative loads.The actuator's motion is driven by a servomotor pump,which gives full play to the advantage of energy-saving.The meter-out pressure is controlled by proportional valves to provide the optimized meter-out damping.The nonlinear adaptive robust control law is designed,which guarantees the control stability and achieve high tracking accuracy.An integrated direct/indirect adaptation law obtains satisfactory parameter estimations and model compensation for asymptotic motion tracking.Comparative experiments under different working conditions were performed to validate the advantages of the proposed control strategy.