Aiming to enhance the seeding accuracy and uniformity of pneumatic maize planters under high-speed operating conditions, and reduce seed collision and deviation during the seed delivery process, a CFD-DEM coupled simulation model was developed based on aerodynamic principles to describe the airflow-induced motion of seed particles within the seed delivery tube. The motion response and force characteristics of seeds under airflow action were systematically analyzed. Considering a representative seed delivery structure, the effects of airflow velocity, structural parameters, and buffer zone dimensions on the horizontal velocity of seeds at the outlet were investigated. On this basis, the Box-Behnken design (BBD) method was employed to establish a response surface model for screening and optimizing key structural parameters influencing delivery performance. Simulation results indicated that a properly designed delivery structure can significantly reduce the frequency of particle-wall collisions and fluctuations in outlet horizontal velocity, effectively achieving “zero-velocity seed release”. Further bench tests of the seed delivery system showed good agreement between the simulation and experimental results, with a maximum error of less than 8%, demonstrating the high predictive accuracy of the proposed CFD-DEM model. The research findings can provide a solid theoretical foundation and valuable engineering reference for the structural optimization of seed delivery systems and the development of precise seed release control strategies in high-speed pneumatic planting devices.