The invention provides a mechanical stretching device for movable sofas, and belongs to the technical field of sofas. The mechanical stretching device comprises a left component, a right component, a switch component and a self-locking spring, the left component is fixedly connected with the right component through a fixing component, the switch component is mounted on the left component or the right component, the left component and the right component are provided with same foot rests, first foot rods, second foot rods, third foot rods, fourth foot rods, small foot rests, mounting side plates, first connecting rods, front linkage parts, fourth connecting rods, sixth connecting rods, rear supporting parts, front supporting parts, linkage part, rear linkage parts, rotating shaft transmission parts, backrest parts, bottom foots, protection parts, third connecting rods and fifth connecting rods, and safe hand clamping prevention devices capable of preventing fingers from being clamped are arranged at the foot rests of the left component and the right component. The mechanical stretching device is simple in structure, convenient to use and reasonable to limit, legs and backrests in an iron stand are more smoothly unfolded and folded, quality grades are improved, and service life is prolonged.