In the rice mill, the negative pressure fan is used to communicate with the air outlet of the rice mill. When rice polishing works normally, high-pressure gas enters the polishing chamber from the spindle, and the gas passes through the sieve plate under the suction of the negative pressure fan and is discharged by the negative pressure fan. Usually, a plurality of air inlets are arranged on the shell of the rice mill. Under the action of the negative pressure fan, part of external air enters the shell through the air inlets and is exhausted by the rice mill. This kind of rice mill has some defects, such as the size of the air inlet is fixed, the negative pressure suction of the negative pressure fan relative to the sieve plate of the rice mill cannot be changed, and it cannot be adjusted according to the processing situation.