Abstract: Abstract: Vacuum-type pneumatic metering device has gradually replaced traditional mechanical seeder and been widely used for corn precision planter in China because of its low damage to seeds and high planting speeds. However, it shows poor adaptability to non-oval seeds such as maize, and requires demanding operating parameters in seed-filling process. Its poor performance of seed-filling often causes high missing rate in field operations. To improve fluidity of seed and performance of seed-filling, many devices that can increase air turbulence, electromagnetic vibration and mechanical agitation have been developed, all of which can complicate the structure of metering device and lead to its performance instability. In this study, a pneumatic maize precision seed-metering device with combined holes was designed by integrating stirring device into the hole to improve performance of seed-filling while remaining the structure and performance stability of metering device. In the device, several curved guide grooves on the seed plate along the circumferential direction formed the combined holes in contact with the annular paries of lower case. With the combine action of guide grooves and positive pressure air flow, seeds were continually rolled down to filling zone area, which could reduce the internal friction among seeds, decrease miss index caused by seed overhead and improve the performance of seed-filling. The equation of guide curve and the structure parameter of the combined holes were determined. The performance of the device was assessed based on multiple index; missing index and seed allocation eligible rates by comparison with traditional vacuum seed-metering device in a field test and a contrast test. A 2BYJMFQC-4 type maize no-tillage precision seeder was used for the field test with a constant pressure of 3.0 kPa and four different forward speeds (3 replicates for each speed test). More than 220 seeds were measured in each test. The PS-12-type pneumatic maize precision seed-metering device with combined holes and the vacuum seed-metering device (Monosem) with a fixed forward speed (10 km/l) were utilized under the same condition in the contrast test. The test was repeated for three times, and 250 seeds were measured in each test. Results showed that the flow of seeds in the pneumatic maize precision seed-metering device was more obvious, and the miss index was only 1.74%, lower than that (3.42%) using the traditional vacuum seed-metering device. The other indexes from the pneumatic maize precision seed-metering device were better than the traditional vacuum seed-metering device at the same working speed. The field test revealed that the qualified index of the pneumatic maize precision seed-metering device had steadily up to 97%. With increasing the forward speed, the missing index and coefficient of variation increased while the multiple index decreased. However, all of the changes in the indexes were small and each index determined from the pneumatic maize precision seed-metering device was better than the national standards of China.