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According to the present situation of the sowing effect of original inside-filling air-blowing seed metering device for flat seeds is better than circles, the phenomenon of drag force greatly affects the cleaning and pressing effect was found through the force analysis of seed in cleaning and pressing process for optimization the sowing effect of circle and mixed seeds. For analyzing the changing of drag force of different seed metering discs in the process of working under the same operational parameter, the bonded particle model was used to model maize based on theory of discrete element method, the coupling analysis method of EDEM-CFD was applied to couple simulation circle seeds with three different hole structures of seed metering discs. The value of drag force of seed in the hole during rotation of seed metering disc was taken as indicator, the changing situation of drag force of seed was analyzed under the operational parameter of inlet air velocity was 30m/s and forward speed was 8km/h with different seed metering discs. Simulation results showed that the drag force of big circle seed was larger than that of small circle due to different particle windward areas in the same type seed metering disc under the same working conditions. In other words, large granular seeds were more likely to be cleaned out of holes. Based on cleaning and pressing performance analysis of different seed discs, the drag force and pressing force in the hole of seed disc with block slot were both larger. And due to the volume of seed filling in the holes was increased compared with other discs, the effect of seed disc with block slot sowing circle and mixed seeds were both better through simulation. The single factor test of working pressure was carried out when forward speed of the different seed discs was 8km/h, experimental results showed that the qualified rate of seed disc with block slot was increased gradually with the increase of working pressure, which was better than the other two. The full factorial experiments were conducted on the seed disc with block slot forward speed of 4~12km/h and working pressure of 4~8kPa, experimental results showed that the qualified rate was increased gradually with the increase of forward speed and working pressure, the qualified rate was close to 96% and leakage rate was less than 1% when working pressure was above 6kPa.