Aiming at stable actuation requirements of the releasing mechanism, an electro-hydrostatic actuator system scheme was proposed. A composite damping adjustment scheme of an end-closed buffer structure combined with throttle valves was designed. Mathematical model of the composite damping system was established. The composite damping structure parameters influence on displacement, speed and damping force of the actuator was studied in the process of releasing the object. The results show that buffer capacity of the actuator is proportional to orifice size of the solenoid valves and the throttle valves. The deviation degree of the ring gap of the buffer structure and the volume of the closed chamber greatly affect the damping performance of the actuator, the ring gap mainly affects the secondary peak value, the volume of the closed chamber mainly affects the cumulative energy conversion of the damping force.