Abstract: In order to meet the requirement of automatic and intelligent development of AFC, aiming at the problems such as complete manual operation, experience control of preload force and insufficient power when tightening chain are existed in hydraulic motor tight chain system of AFC at present,an automatic tight chain system was designed. By arranging electromagnetic clutch in the transmission device of scraper conveyor, the system can realize the controllable clutch between the hydraulic motor tension chain device and the transmission system；And the speed sensor and pressure sensor were arranged on the hydraulic motor to make the output of the tension chain force accurate and controllable.In order to adapt to the needs of actual working conditions, the hydraulic motor tension chain system should have the ability to drive the overload AFC in order to remove part of the overloaded coal. Around the above functions of hydraulic motor automatic tension chain system, the system construction, parameter setting and hydraulic motor selection were analyzed and discussed.