Abstract: Underwater hydraulic technology is widely used in deep-sea exploration and resource exploitation. In order to eliminate the influence of seawater pressure on the hydraulic system, improve the efficiency of the system, pressure compensation technology is commonly used in hydraulic systems. As a key element of pressure compensation technology, the pressure compensator has been designed on the basis of experiences. In this paper, the software AMESim is used to simulate the underwater hydraulic system and it is obtained that the influence of structural parameters of compensator and hydraulic system parameters on hydraulic system. While the preloading pressure is the same, the greater the spring stiffness of the compensator, the faster the pressure of the compensator decreases, and the smaller the differential between the pressure of the tank and the environment pressure. The larger the inner diameter of the compensator, the smaller the peak of system pressure fluctuation. Due to the load, the pressure on both sides of the cylinder is likely to be lower than that of the environment pressure, and the water enters the cylinder. Adding the throttle valve at both sides of the cylinder to control the speed of it can significantly increase the pressure on both sides of it, and improve the sealing reliability of the system.