Abstract: The pheumatic seed metering device is a key component of precision drill, which performance direct affect the quality of seeding. A theoretical analysis was conducted on the adsorption mechanism of the pheumatic seed metering device and an air flow field equation has been derived. An analytical calculation of the state of seed subjected to force under suction effect and the seed motion after breaking away from suction hole was carried out, and a seed motional equation was established. A single factor experimental of the pheumatic seed metering device on the soybean seeding process, taking the rotation speed of seed metering disk and the vacuum degree in suction chamber as experiment factors respectively, was carried out on the experiment stand. The experiment results show that: When the rotation speed of seed metering disk exceeds the one for the vacuum degree to suit for obtained by theoretical calculation, the performance quality gets worse and miss seeding rate evidently increases up to 29.63%; When the vacuum degree in suction chamber is 2.5 kPa, the miss seeding rate will increase up and the seeding rate up to standard appears descending tendency with the rotation speed of seed metering disk increasing; When the rotation speed of seed metering disk is kept at 54 r/min and the vacuum degree in suction chamber is higher than 1.5 kPa, the seeding rate up to standard ranges from 76.11% to 80.65%; When the vacuum degree in suction chamber is lower than 1.5 kPa, the seeding rate up to standard obviously decreases .