The utility model provides a weed chopper for tree trunks in orchards. A frame is arranged on one side of an oil tank, an input shaft bearing seat, an oil pump and a rotary fulcrum are arranged on the frame, a cutter shaft is arranged on the rotary fulcrum through a cutter shaft supporting installation seat, blades are connected onto the cutter shaft through a cutter shaft support at intervals, a cutter shaft oil seal seat is arranged at one end of the cutter shaft, and the other end of the cutter shaft is connected with a hydraulic motor through a coupler and a motor installation seat. An oil pump driving chain wheel is arranged at one end of an oil pump output shaft and is in transmission connection with a driving chain wheel of an input shaft arranged in the input shaft bearing seat through a chain, and the input shaft is connected with a transmission shaft. A hydraulic distributor is arranged on one side of the frame, a rotary oil cylinder is arranged on the hydraulic distributor, a copying rotary valve is arranged at the upper end of the rotary oil cylinder which is in transmission connection with the cutter shaft through a copying bar, and a suppression rotary drum is arranged at the upper portion of the copying bar. The weed chopper can clear weeds in tree trucks to return weeds to fields and be suitable for serving as the weed chopping machine for tree trunks in orchards.