The utility model discloses a mechanical hand for replacing a slag blocking gate valve mechanism. The mechanical hand comprises a clamping body, two clamping claws, two clamping hydraulic cylinders, a rotary gear ring bearing, a rotary joint, a telescopic inner arm, an outer arm, a telescopic hydraulic cylinder and a rotary motor, wherein the clamping body is provided with a front end and a back end, the front end of the clamping body is provided with an upper end and a lower end, each clamping claw is respectively provided with a clamping end and a tail end, the two clamping claws are respectively hinged with the upper end and the lower end of the clamping body, the two clamping hydraulic cylinders are respectively and correspondingly connected with the tail ends of the two clamping claws and drive the clamping ends of the two clamping claws to move in the same direction or the opposite directions, the end surface of an outer gear ring of the rotary gear ring bearing is fixedly connected with the back end of the lamping body, the rotary joint is arranged in the rotary gear ring bearing, the telescopic inner arm is provided with a head end and a tail end in the axial direction, the head end is fixedly connected with the rotary joint, the telescopic inner arm is in coaxial arrangement with the rotary gear ring bearing and the rotary joint, the outer arm is sheathed outside the telescopic inner arm, the telescopic hydraulic cylinder is connected with the telescopic inner arm so that the telescopic inner arm is driven to slide in the outer arm along the axial direction, and the rotary motor is connected with the outer gear ring of the rotary gear ring bearing.