The invention discloses a quick replacing mechanism for a mechanical hand clamp. The quick replacing mechanism comprises a fixed column and a fixed sleeve. The lower end of the fixed column is provided with a notch, the fixed column is provided with a plurality of steel ball holes, the steel ball holes are communicated with the notch, steel balls are arranged in the steel ball holes, the inner sides of the steel ball holes are provided with ball blocking parts, the fixed sleeve comprises a sleeve body part matched with the notch and a limiting part, and the outer surface of the sleeve body part is provided with a plurality of clamping grooves which are of an arc-shaped structure. When the fixed sleeve is connected with the fixed column, the inner sides of the steel balls are clamped in the clamping grooves, the lower end of the fixed column is fixedly connected with a fixed ring, the fixed column is provided with a baffle ring, a positioning sleeve is vertically movably arranged on the fixed column between the fixed ring and the baffle ring, a spring is arranged on the fixed column between the positioning sleeve and the baffle ring, the upper portion of the inner side of the positioning sleeve is provided with an abutting-against part, the lower portion of the inner side of the positioning sleeve is provided with a plurality of accommodating grooves, and the accommodating grooves each are of a conical structure. According to the quick replacing mechanism for the mechanical hand clamp, the clamp can be quickly replaced, the operation is convenient and simple, and working efficiency is improved.