Partial body-weight supported gait training is an important rehabilitation means in curing lower extremity walking drawback resulting from nerve diseases. As the patient is unable to support his/her own body weight and keep the body in balance during the treadmill training, the body weight support system that help the patient reduce the body weight and keep the body in balance is import for rehabilitation equipment. This paper describes a control method for the body weight support system designed in the laboratory, builds a control system and demonstrates its feasibility by experiments. Experimental results show that the proposed method can meet the requirements of the body weight support system.