Simulation of the gas-solid flow in an inside-filling air-blowing maize precision seed-metering device was performed by means of a coupling approach of the discrete element method (DEM) and computational fluid dynamics (CFD). In this model, EDEM software was used to depict the discrete particle phase, and ANSYS Fluent software was used to describe the continuous gas phase. Maize particles were created by EDEM software using the bonded particle model (BPM) to define a single structure of the particles. Effects of the positions, the width and the average arc length of the lateral hole were examined and analyzed in terms of gas field and seed movement. Using an orthogonal experimental design, the primary and secondary factors and parameters of the maximum evaluation index affecting the working performance of a seed-metering device were assessed. The superiority of a lower position of the lateral hole was identified, as both the width and the average arc length of the lateral hole had no effect on the drag force or differential pressure. The area of the lateral hole significantly affected the movement and airflow field of seeds in the hole of a seed-metering device. The drag force, the differential pressure and the pressure loss increase with the expansion of the area of the lateral hole also resulted in a decrease in the upper pressure. The optimized lateral hole, which is 1.5 mm wide and has an average arc length of 10 mm when the position is lower, had a good working performance, with less pressure loss, superior drag force and differential pressure. The qualified rate of the optimized seed-metering device was greater than 93% when the working pressure was above 5.5 kPa with a working speed lower than 10 km/h through experiment. The results showed that the DEM-CFD coupling approach was a reliable instrument for simulating the physical phenomenon of seed movement in the airflow field. DEM-CFD coupling simulation of seed movement can provide a theoretical basis for assessment of the potential working performance of an inside-filling air-blowing seed-metering device.