Abstract: Disclosed are a position locking method of an underwater equipment, a terminal device, a system and a medium. The method comprises: acquiring an optical image and a sonar image taken by an underwater equipment; obtaining a target image by synthesizing the optical image and the sonar image, the target image including at least a target object; determining position offset information of the target object according to the target image; and generating position control parameters of the underwater equipment according to the position offset information, and sending position control parameters to the underwater equipment to make the underwater equipment to lock a position according to the position control parameters. The present application greatly reduces operation difficulty of the underwater equipment in turbid or undercurrent water areas.