The invention discloses an automatic belt tension regulating device of a coal feeder. The automatic belt tension regulating device is characterized by comprising a control assembly and a regulating assembly, wherein the regulating assembly comprises a reduction gear and a tightening roller, and one end of a tightening roller core shaft is provided with a sliding block; a main gear of the reduction gear is connected with a motor, a driven gear is connected with one end of a tightening rod, the other end of the tightening rod is arranged in a pair of tightening rod guide rails and connected with the sliding block at one end of the tightening roller core shaft, and the sliding block is arranged in the tightening rod guide rails; the moving direction of the tightening rod is perpendicular to the tightening roller core shaft; the control assembly comprises a tightening wheel and a proximity switch, and one end of the tightening roller core shaft is provided with a sensing block; the proximity switch related with the sensing block is connected with the motor through a relay. The automatic belt tension regulating device of the coal feeder is accurate, reliable, free of manual operation, and capable of automatically regulating belt tension of the coal feeder.