The screw jack, also known as the mechanical jack, is driven by a manpower through a screw pair, and a screw or nut sleeve is used as a jacking member. The ordinary screw jack supports the weight by the thread self-locking function, and the structure is simple, but the transmission efficiency is low and the return stroke is slow. The thread of the self-propelled screw jack has no self-locking action and is equipped with a brake. Relax the brakes, and the weight can be quickly lowered by itself, reducing the return time