Underwater docking devices can be connected with the AUV, and then supply the AUV with energy and exchange data with it. Aiming at the characteristics and shortcomings of the existing docking technology, a new type of underwater docking device which was suitable for large-depth submarine environment was proposed. In view of the problem that the traditional oil hydraulic technology polluting the marine environment due to the leakage in the sea, a hydraulic system scheme with water-glycol hydraulic fluid as the working medium was developed. In order to realize the automatic action of the docking device, the control system was designed. To study the performance of the control system, the mathematical model of the asymmetric hydraulic cylinder of the locking circuit was derived. On this basis, the overall mathematical model of the system was drawn and MATLAB/Simulink simulation was made, and the PID control algorithm was used to improve the performance of the control system.