In order to solve the problem in vegetables seed-metering device that the seeding quality decreased due to multiple grains in one hole during seed suction, a four-stage sawtooth for seed cleaning was proposed and a four-stage seed cleaning mechanism was designed. The reasons for the phenomenon of resuction were expounded, and a mathematical model was established to determine the key parameters such as the installation position and tooth profile angle of the seed clearing mechanism. The distance between the top of the tooth and the mold hole, the working speed of the seed dispenser and the negative pressure of the chamber were selected as the main factors to carry out the quadratic regression orthogonal rotation combination test. The significance and regression analysis of the test results were carried out. The optimal parameter combination was obtained as the distance between the top of the tooth and the mold hole of the 4th seed dispenser was 0.41mm, the negative pressure was 1.22kPa and the working speed of the seed dispenser was 5.85r/min. The verification test and comparison test of the optimal working parameters were carried out. The verification test showed that when the working speed was 4.5~9.5r/min, the leakage rate was not more than 1.50%, and the overclearing rate was not more than 1.88%, which was basically consistent with the calculated value of the regression equation. The comparative test showed that when the rotation speed was 4.5r/min, 7.0r/min and 9.5r/min, the leakage rate of the four-stage seed clearing mechanism was reduced by 3.2 percentage points, 4.0 percentage points and 5.0 percentage points, the overclearing rate was reduced by 0.19 percentage points, 0.83 percentage points and 1.45 percentage points, and the qualified rate of seed discharge was increased by 3.42 percentage points, 4.83 percentage points and 6.45 percentage points, respectively. The four-stage seed cleaning mechanism can effectively reduce the leakage rate of seed cleaning link and improve the working quality of seed discharging device.