Abstract: Abstract: Narrow-row-dense planting technology of soybean can generally increase production by more than 15% compared with conventional ridge cultivation. However, it has less research on this model and supporting equipment in the Huang-huai-hai area. At present, the traditional soybean planter has such problems as large sowing distance, poor seed-metering performance, poor stability of the device and complex structure. Due to the above problems, it's difficult to meet the requirement of narrow-row-dense planting operation of soybean. Therefore, a novel design of a pneumatic seed-metering device with single seed-metering plate for double-row was presented, which could realize 120 mm narrow-row spacing sowing together with the distributor. Despite a large number of study of other seed-metering devices, this pneumatic seed-metering device with single seed-metering plate for double-row could overcome the traditional limitations of regulating the row spacing by adjusting spacing between left and right monomers or mounting the monomers front and after. In addition, the row spacing could be changed through the use of different angle distributor, which was impossible for other seed-metering devices. Its basic structure and working principle were analyzed. It could determine the influence factors of seed-metering performance through the mechanical and dynamic analysis of the movement of seeds in filling zone, carrying zone and outside throwing point. To verify the feasibility of 120 mm narrow-row spacing sowing, the test device of pneumatic seed-metering device was built, which included the conveyor belt, seed-metering device, suction belt and transmission system, and the whole structural working mechanism of the machine was introduced in detail in this research. Three parameters, i.e. negative pressure vacuum, seed-metering plate's rotational speed and suction holes number of each lap were chosen as the influence factors of the test experiment. And the test index included leak seeding index, repeating sowing index and qualified index of inner and outer which could represent the seed-metering performance of the seed-metering device. Through the single factor experiment, the impacts of three factors were analyzed. Reasonable variation rage of various factors for better seed-metering performance was determined, while the negative pressure vacuum raged from 4.5 to 5.5 kPa, the seed-metering plate's rotational speed raged from 15 to 21 r/min and the suction holes number of each lap was changed in 3 levels of 56, 64, 72 in turn. According to the single factor test results, three-factor and three-level orthogonal experiment was carried out. The results showed that the factors had significant influence on the seed-metering performance of the outer and inner, and the inner was always better than the outer. The order of influence factors on qualified index was seed-metering plate's rotational speed, negative pressure vacuum and suction holes number of each lap; the order of influence factors on repeating sowing index was negative pressure vacuum, seed-metering plate's rotational speed and suction holes number of each lap; the order of influence factors on leak seeding index was negative pressure vacuum, seed-metering plate's rotational speed and suction holes number of each lap. The optimal conditions were as below: the suction holes number of each lap was 64, the seed-metering plate's rotational speed was 18 r/min and the negative pressure vacuum was 5 kPa. Under the above conditions, the inner qualified index was 98.45%, the inner repeating sowing index was 0.72% and the inner leak seeding index was 0.53%. In addition, the outer qualified index was 97.82%, the outer repeating sowing index was 0.63%, and the leaking seeding index was 1.35%. The verification test showed that the seed-metering device had good performance and the test index was better than this given in industrial standard. This research provides a reference for the research and development of pneumatic seed-metering device for the soybean narrow-row and close planting seeder.