Considering the problem that the pressure gradient change direction in mixing component does not match with seed conveying direction during seeding process, causing backflow and counterflow of seeds, which leads to each row seeding uniformity of centralized metering lower, a prototype of mixing component based on Venturi principle was developed. The main structure and key parameters of the Venturi mixing seed chamber and conveying seed tube were determined. The effects of airflow velocity, seed velocity, and structure of mixing component on total pressure loss were analyzed. The DEM-CFD coupled simulation was used to compare and analyze the effects of three kinds of conveying seed tube and two kinds of Venturi mixing seed chamber on seed migration trajectory, airflow pressure distribution and conveying seed performance. The simulation results showed that the combination of Venturi mixing seed chamber with accelerating mixing section and the conveying seed tube with elbow joint had better conveying seed performance, and the variation coefficient of seed quantity consistency of each area for rapeseed and wheat in the vertical section of conveying seed tube was 9.63% and 13.43%, respectively. The intelligent test platform for planting machines was used to carry out the test of the effect of better combination of mixing component on the seeding performance. The bench test results indicated that the backflow rate of rapeseed was less than 3.2%, there was no counterflow of rapeseed, and backflow and counterflow of wheat seed. The uniformity variation coefficient of seeding quality of rapeseed and wheat was less than 5% and 3.9%, respectively. The stability variation coefficient of total seeding quality of rapeseed and wheat was less than 1.15%% and 1.35%, respectively, which met the performance requirements of rapeseed and wheat seeding. The research can provide a reference for the structure improvement of the mixing component of airassisted centralized metering device.