The invention provides a duplex tooth production device of a high-precision speed reducer for a robot and an application method thereof. The device comprises a laser welding device, a laser rotating support, a rotating mechanism, a rotating platform and a speed reducer main body, wherein the center of a central gear is fixedly connected with a rotating shaft; and a duplex gear A, a duplex gear B and a duplex gear C are evenly arranged around the central gear; the gear outer portions, connected with the central gear, of the duplex gear A, the duplex gear B and the duplex gear C are connected with an output gear ring through gears; a fixed gear ring is arranged above the output gear ring; a rotating frame is arranged at the end, close to the top of the speed reducer, of a rotating shaft of the duplex gear A, a rotating shaft of the duplex gear B, a rotating shaft of the duplex gear C and the rotating shaft of the central gear; a rotating frame welding gap is formed in the position, between every two rotating shafts, of the side edge of the rotating frame; the rotating mechanism is arranged in the center of the rotating platform, and the rotating mechanism is fixedly connected with the rotating shaft of the central gear; the laser rotating support is arranged on the rotating platform and close to the side surface; and the laser welding device is arranged on the top of the laser rotating support. The duplex tooth production device and the application method thereof have the beneficial effect of improving the machining precision of the speed reducer for the robot.