The invention discloses a coarse grinding device. The coarse grinding device comprises a first support plate, wherein a second support plate is arranged in rear of the first support plate; a base plate is arranged above the first support plate and the second support plate; a rotary motor is arranged on the lower surface of the base plate; a connecting plate is arranged at the upper end of the rotary motor; a placement block is arranged at the upper end of the connecting plate; a first vertical plate is arranged on the left side of the placement block; a second vertical plate is arranged on the right side of the placement block in a manner of being symmetrical with the first vertical plate; an air cylinder mounting plate is arranged in rear of the placement block; a grinding cylinder is arranged on the upper section of the rear surface of the air cylinder mounting plate; a grinding rod is arranged at the front end of the grinding cylinder; pressure rod mounting holes are formed in the peripheral side wall of the placement block; and a pressure rod is arranged in each of the pressure rod mounting holes. The coarse grinding device has the advantages of being simple in structure, convenient to use, small in size and easy to carry.