The utility model relates to a speed reduction joint control device of a rotor spinning machine. The speed reduction joint control device comprises a spinning apparatus, a rotor, an induction electromagnet, a proximity switch, a spinning apparatus pad plate, a rotating shaft, a cotton feeding device, a doffing device, a winding device, a broken yarn detector, a rotor motor and a tangential belt, wherein the induction electromagnet is bonded on the spinning apparatus, the spinning apparatus pad plate is connected with the proximity switch, the spinning apparatus is in rotary closing with the spinning apparatus pad plate through the rotating shaft, meanwhile, the speed reduction joint control device also comprises a controller, and the controller is connected with the proximity switch, a winding motor, a doffing motor, a cotton feeding motor and the broken yarn detector. The speed reduction joint control device has the advantages that when the spinning apparatus is closed, the induction electromagnet is in contact with the proximity switch, control program is triggered, meanwhile, the rotating speed of the rotor is gradually increased to constant speed from zero, the rotor speed at the joint moment is determined by an electric control system according to delay time setting, and the characteristic that a joint is still at low rotating speed when the rotor is at high speed is realized, so the success rate of the joint and the quality of the joint are improved.