The invention provides a main winch speed reducer test bed. The main winch speed reducer test bed comprises a speed reducer body, a baffle, a test bed plate, a coupling I, a coupling II, a motor, a telescopic protecting plate, a fan, a lead screw, an L-shaped protecting plate and an electric motor, wherein the baffle is fixed on the outer end surface of the speed reducer body, the baffle and the speed reducer body are assembled on the upper end surface of the test bed plate, the right end of the speed reducer body is connected with the coupling I through an input shaft, the coupling II is fixed on the right end surface of the coupling I, and the motor is assembled to the right end of the coupling II. The design is convenient to assemble and easy to operate; the electric motor is assembledto the right end of the L-shaped protecting plate, the lead screw is welded to the left end of the electric motor, the telescopic protecting plate is mounted at the left end of the lead screw, and thefan is arranged on the lower end surface of the telescopic protecting plate, so that the protecting effect is improved; and the main winch speed reducer test bed is convenient to use and operate, canbe rapidly mounted and has a good protecting effect.