The wheat/maize flow into the first sieve surface through feeding entrance. Inside this surface, large impurity on the upper sieve is discharged to the hopper. The wheat/maize through first sieve surface to the second sieve surface for continual filter. Inside this surface, the material separate by upper sieve surface. The small impurity is dischargedon the soleplate straightly, the clean stock on the upper sieve surface come to the discharging hopper through the suction road.