The underwater toolkit switching device is mainly used for connecting the hydraulic source of underwater tools and remotely operated vehicles（ROVs）, and provides hydraulic power for underwater tools. A new switching device was designed to realize the non-pollution connection under water of two groups of hydraulic circuits. The docking process between the male assembly and the female assembly of the switching device was simplified as the docking process between the hole and the axle. The ADAMS software was applied to simulate the docking process under the given parameters. The results show that the contact force is larger when the angle deviates.