In order to solve the problem of high multiple index of air-suction metering device and the difficulty in ensuring the rationality of design of clearing mechanism, the seed clearing mechanism of air-suction metering device was optimized. By defining the concept of the ratio of diameter of hole occupied by the seed when it was adsorbed, the mathematical model of the clearing process was established, the mechanism of the clearing process was analyzed, and the ratio of the minimum diameter of the hole occupied by the seed when it was adsorbed was obtained. The change of linear velocity of seed plate type hole was not obvious, but it was decreased obviously with the increase of type hole diameter. The installation position, chamfer of sawtooth edge and clearing curve of the clearing mechanism were analyzed and designed respectively. A parametric mathematical model for designing the clearing mechanism of air-suction metering device was established. The key factors affecting the shape of the clearing mechanism were seed size and radius of the type hole in the seed plate, while the linear velocity of the seed plate had little effect. In order to simulate and record the trajectory and parameters of any particle at any position and accurately simulate the working details of the seed cleaning process, the DEM-CFD coupling simulation method was used to simulate and analyze the seed cleaning process. By extracting the speed change index and observing the change of seed speed, the impact of seed cleaning mechanism on seeds was obtained. It was verified that the designed clearing curve can play a good role in clearing seeds step by step. The order of impact force of seed cleaning from large to small was large flat, small flat and round shape. Choosing Zhengdan 958 non-graded seeds and the optimized clearing mechanism was compared with the previous metering device. In order to ensure the same working conditions, the same air pressure of -3kPa was used to carry out the experiment. Three times of test data were selected to take the average results. The result showed that the qualified index after optimization had a certain degree of improvement compared with that before optimization, and with the increase of operation speed, the rising extent of qualified index was increased, and the optimized multiple index was decreased significantly. This trend was increased with the increase of speed, and the missing index did not increase with the decrease of multiple index, but it was decreased slightly while maintaining the original level of missing index. The optimized metering device was operated at speed of 8~14km/h, the qualified index of the optimized metering device was not less than 92.0%, the multiple index was not more than 1.6%, and the missing index was not more than 6.3%. The optimized clearing mechanism can reduce the seed missing while reducing the multiple index, effectively improve the qualified index, and verify the rationality of the mathematical model design of clearing mechanism parameters. The maize seeds of Zhongke 11, Zhengdan 958 and Zhongyuandan 32 were selected for the comparative experiment at the speed of 14km/h. The results showed that they had good adaptability to different varieties of seeds. This model can design clearing mechanism according to different seeds and metering device sizes, which provided a basis for the design of air-suction metering device clearing mechanism.