A numerical study of gas-solid flow in seed feeding device of air-assisted centralized metering system was carried out by means of Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) coupling approach. In this model, discrete particles phase was applied by EDEM software and continuum gas phase was described by ANSYS Fluent software. Effects of throat’s area, throat length, airflow inlet velocity and seed feed rate were studied and analyzed in terms of gas field and seed movement. Simulation results showed that, throat’s area and airflow inlet velocity mainly affected airflow outlet velocity and seed velocity of airflow direction which resulted from drag force, while seed movement was affected by throat length and seed feed rate slightly. The increase of throat area resulted in the decrease of seed velocity and pressure loss in a certain range. Seeds moved slowly and generated the phenomenon of bounce and concentration for low airflow inlet velocities. With the airflow inlet velocity increased, resultant force and seed velocity developed. The proper airflow inlet velocity was 16–20 m/s and 20–24 m/s for rapeseed and wheat, respectively. It showed that DEM-CFD coupling approach is reliable as a tool for understanding the physical phenomenon of seed movement in airflow field. Numerical simulation of seed motion based on DEM-CFD coupling approach can provide theoretical basis for developing operating performance of seed feeding device.