The utility model discloses a tensioning device for a transmission belt of an air condition compressor of an excavator. The tensioning device for the transmission belt of the air condition compressor of the excavator comprises an engine belt wheel, the transmission belt and the air condition compressor and further comprises a fixing support frame and a rotating support frame, wherein a sliding groove is arranged in the upper end of the fixing support frame, and the upper end of the fixing support frame is connected with the upper end of the rotating support frame through the sliding groove in a sliding mode. The lower end of the fixing support frame is connected with the lower end of the rotating support frame in a hinged mode, and the air condition compressor is installed on the rotating support frame. A tensioning bolt and a locking nut are arranged at the upper end of the rotating support frame. According to the tensioning device, a tensioning wheel is spared, and a compressor belt wheel and an engine driving wheel are easy to center. The tensioning device for the transmission belt of the air condition compressor of the excavator is easy to adjust, few in fault points, capable of effectively prolonging the service life of the transmission belt and improving the reliability of an air conditioning system and beneficial to normal operation of a main engine.