The invention discloses a large granulating unit machine head locking device which comprises a machine head body, a position sensor, a sensor sensing frame, locking blocks, a moving frame, movement air cylinders, a guide frame and a pneumatic control system. The position sensor, the moving frame and the guide frame are arranged on the machine head body. The sensor sensing frame and the locking blocks are arranged on the moving frame. The piston rod ends of the movement air cylinders are connected with the moving frame, and the fixed ends of the movement air cylinders are connected with the machine head body. According to the large granulating unit machine head locking device, the locking blocks are pushed through the air cylinders on the two sides of the machine head body to move up and down in the vertical direction, the locking blocks are rapidly moved, manual operation is thoroughly avoided, the acting direction of the air cylinders is automatically controlled by the pneumatic control system, manual misoperation is eliminated, the locking blocks are controlled to be in locked and opened positions through signal feedback of the sensor sensing frame and the sensor, the locking blocks are in place accurately, and the movement track of the locking blocks is limited in the vertical direction always through the guide frame.