To improve the uniformity of the forage seed metering, a 3-D model was built to simulate air-stream distributive metering device using computational fluid dynamics (CFD) method, in which the distribution of airflow field and path curve of the particle phase were simulated using standard k-εmodel and discrete phase model (DPM), respectively. The results of simulation were in good agreement with experimental data. However, in the simulation, a few seeds were left in the distributor due to the air vortex, which impairs the uniformity of seed sowing. Therefore, CFD simulation was conducted to improve the structure of distributor, and vortex-caused seed detention was finally avoided after the improvement.