This paper presented a novel underwater electromechanical docking technology used on the underwater self-reconfigurable robot. The multi-jaw mechanical device and oil seal method were applied, which realized reliable mechanical and electrical connection. The robotic inverse kinematics was studied in joint coordinated control, which was used for tracking the end module while docking. The signal optimization algorithm for photoelectric sensors was applied to assist underwater docking. The underwater docking device and prototype of underwater selfreconfigurable robot based on the device were developed. The application on USR verified the validity of the technology.