Gravity separator is important equipment for seed separating processing. Aiming at that seed entering the separating table from disordered state to layered state occupied the area of the separation table, which affected the separating performance and made the adjustment more difficult, the prestratification technology of seed entering the separation table was put forward and the matching stratified feeding system was developed. The system was installed on the “5TZX-50 gravity separator”, which was located between the feed system and the separating table，and it was fixed with the separating table. It was mainly composed of a feeding hopper, a laminar grid, a guide board, a stratified net, and a wind tube. The feeding hopper received the seeds of the feeding system, and the stratified net transmitted the separating seeds to the separating table. The stratified feeding system was a vibrated feed machine and also a material suspender. The system vibrated synchronously with the separating table to complete the seed transport, while the system gave the seeds suspended air flow to stratify the seed. The key parameters obtained were: inclination angle of feeding hopper was 54°, laminar grid length was 8.5mm, width was 8.2mm, and stratified net inclination angle was 26°. The system model was established in SolidWorks, and the maximum acceleration was applied to the model by SolidWorks-Simplation, and the working stress and displacement were analyzed. The flow field was simulated by SolidWorks-Flow Simulation, and the flow velocity distribution, static pressure field distribution, and ion flow traces on flow field were obtained. Inclination angle of the guide board was optimized with the minimum entrance pressure as the optimization condition. Through the verification test, the Box-Behnken response analysis was carried out by the DesignExpert software，also using the variance analysis of the regression model，the mathematical regression model of performance indexes and influencing factors was established, the obtained best combination was flow velocity of 3.40m/s, vibration frequency of 9.75Hz and inclination angle of 29.65°. The results showed that range of errors of separating rate of impurity and target optimization predictive value was not more than 1.36%. The stratified feeding system can improve the impurity removal performance of gravity separator. For the low density impurity removal rate, the effect of airflow speed of stratified feeding system was greater than that of vibration frequency; for the high density impurity removal rate, the effect of vibration frequency of stratified feeding system was greater than that of airflow speed. The stratified feeding system reduced the influence of airflow speed on the high density impurity removal rate, and reduced the influence of vibration frequency on the low density impurity removal rate, thus reducing the difficulty of adjusting gravity separator. The research can provide theoretical basis and technical support for the design of stratified feeding system of gravity separator.