To explore the influence of gravity assist on the filling performance of the vacuum precision seed-metering device with synchronously rotating seed plate and vacuum chamber, taking the vacuum precision seed-metering device as the carrier, stress analysis of filling process was carried out, and mathematical model of gravity-assisted filling was shown. The results showed that gravity radial component along the seed tray was consistent with direction of dragging force, during the filling process;gravity radial component along the seed tray was consistent with direction of pressure gradient force, during filled seeds detachment process from population. Effects of different numbers of seeds to be filled seed on average normal force of seed tray under low, medium and high states were analyzed by simulation using engineering discrete element method (EDEM) software. Simulation results showed that average normal force was not changed significantly within low, medium and high states under population of 300;the average normal force was varied within low, medium and high states under population of 600, 900 and 1200, the influence of the population on the filling effect can be neglected. Laboratory tests results showed that missing index of seed-metering device from big to small was satisfied as low condition, medium condition and high condition. Comparison test between gravity-assisted filling and non-gravity-assisted filling of the seed-metering device showed that qualified index was above 94% under operating pressure of 3~5.5kPa with gravity-assisted filling, which met national standard under operating pressure above 6kPa with no gravity-assisted. Gravity-assisted filling significantly reduced operating pressure demand and improved the quality of work.