Abstract: Mechanized transplanting can contribute to increasing the crop yield with high efficiency in the Yangtze River Basin of Southeast China. In this study, a novel pneumatic seed-metering device was designed to precisely control the plug seedlings and mechanized transplanting with potted trays in rapeseed production. The specific structure of the seed-metering device with a pneumatic roller planter was optimized to obtain the suitable operating parameters for better rapeseed growth and yield. The performance of the seed-metering device was investigated under laboratory and field conditions for rapeseed planting. A new integrated optimization technique on the Fluent software was used to simulate the internal flow field under three types of distance between the holes of the air inlet, where the inner wall of the roller and the seed suction hole contacted with the positive pressure chamber. A systematic investigation was made on the key components in experiments to determine the optimal ranges of the principal factors affecting the seeding performance. A field test was conducted to evaluate the adaptability and precision of the seed-metering device for rapeseed plug seedlings. An orthogonal combination test was carried out to analyze the relationship between three main influencing factors(negative pressure, positive pressure and diameter of seed suction hole) and seed performance (single seed qualified index, miss seeding index, and multiple seed index). A response surface method was selected to obtain that the primary and secondary factors affecting the single qualification index were a positive pressure, the diameter of seed suction hole, and the negative pressure. The influence of the other two parameters on the single seed qualified index presented a trend of first rising and then falling when one of the parameters was fixed. The results showed that there was no backflow in the positive pressure chamber, where the spacing of the air inlet was 144 mm, and the airflow velocity was relatively uniform at each hole of the seed suction hole. The optimization of multiple objective variables was selected to obtain the optimal parameters in the Design-Expert software. Three primary influence factors were achieved, including the negative pressure(3.73 kPa), positive pressure(0.23 MPa), and diameter of the suction hole(1.28 mm). In this case, the single seed qualified index reached 95.13%, the seed missing index was 2.80%, and the multiple seeding index was 2.07%. Taking three varieties of rapeseed and an alien vegetable seed(eggplant) as the examples, the adaptability and metering performance of pneumatic seed-metering device were evaluated, when the productivities were 600, 700, or 800 trays/h, respectively, where the negative pressure, positive pressure and diameter of seed suction hole were set as 3.60 kPa, 0.23 MPa, and 1.20 mm, respectively. In rapeseeds, the single seed qualified index was higher than 93%, while the seed missing index, and multiple seeding index were less than 5%. In vegetable seeds, the single seed qualified index was higher than 90%, and the seed missing index and multiple seeding index were both less than 5%. It infers that the seed metering performance of the pneumatic seed-metering device was accurate, efficient and adaptable for rapeseeds and other vegetable potted tray raising seedlings. The findings can serve as a promising reference for the development of rapeseed tray raising seedling, and mechanized transplanting in most vegetables.