Abstract: Taking the locking mechanism of a certain type of mobile crane's movable support leg as an example, this paper analyzes the locking structure, locking process, and existing problems of the mobile crane's movable support leg. In response to its existing problems, based on the traditional automobile crane leg control system, the structure, electrical system, and hydraulic system of the leg automatic locking device were optimized using sensors and hydraulic transmission technology. A leg automatic locking device was designed to achieve automatic locking of the movable leg and the fixed leg, thereby avoiding potential safety hazards and equipment damage caused by human factors. Through trial production verification, the scheme is feasible, easy to modify, and highly reliable, which can provide reference for the design of similar devices.