Abstract: Abstract: Combined with the good filling performance of the inside-filling seed metering device, in this study, one kind of combined nozzles was designed using the principle of gas cleaning of air-blowing seed metering device and the principle of pressing seeds of air pressure seed metering device. At the same time, the semi disc structure of seeding plate was used. The conical stepped hole was adopted in the form of hole, so as to achieve the seed charge under self-gravity. The obliquity of combined nozzles was designed as 75°, the distance between the intersection of the center axis of clearing nozzle and the horizontal direction of the center of seeding plate and vertical direction of the center of seeding plate was about 45mm through the design calculation of the structure and position size of combined nozzles. The function and necessity of pressing nozzle was determined through the comparison of fluid simulation of single cleaning nozzle and combine nozzles. We concluded that the flow velocity of the outlet was at least 11.7 m/s to satisfy the cleaning condition through the analysis of the force of the seed in the hole during cleaning process. The outlet air flow speed was increased by reducing outlet area of cleaning nozzle due to the outlet velocity of the air nozzle was inversely proportional to the outlet area. Finally, the outlet area was defined as 1/3 of the total area of cleaning nozzle. By means of the fluid simulation of gas nozzles with different cross sections, this research produced that the larger inclination angle of cleaning nozzle, the larger area of high speed air flow which generated by the gas nozzle in the whole chamber and which was more difficult to produce vortex in the rear side hole. The differential pressure generated by the gas nozzle with 45° in the hole was the largest by detecting the pressure value of the upper and lower part of the hole with different dip angles. Therefore, the single seed was the most easily attached to the inside of the hole under this inclination angle gas nozzle. According to the simulation results, the angle between the section of nozzle and the pipe wall was 45°. The bench tests were carried out on the seed metering device according to the performance indexes such as working pressure, replay index, leakage index and the qualified rate of grain distance. Experimental results showed that the qualified index was above 86.58% which the effect was not the best under the working pressure was 5 kPa or above when the seeds were not graded. Through the classification of maize seeds and seeds of different types of the qualified index of different kinds of seeds basically had such regular: big flat>small flat>small circle>big circle through the classification of maize seeds. The qualified index of big flat could reach more than 95% under the pressure of 4.5 kPa and the small flat seeds could also achieve the same sowing condition under the pressure of 5.0 kPa. The theoretical foundation was provided for the improvement research of the following seed metering device through analyzing the reasons of replay leakage of flat and circle seeds combined with high speed imaging technology.