Considering at the problem of small particle size and light quality of rapeseed, which makes it difficult to displace individual seeds, a positive and negative pressure combination roller type precision seed-metering device was designed. The working principle of the seed-metering device was clarified, and the force analysis of the seed absorbing, seed carrying and seed discharging links of the seed-metering device was carried out, as well as the analysis of the dragging process of the seed discharging roller on the seed population. The mechanism of preventing dragging accumulation by controlling the height of the seed layer in the seed filling area and the pressure of the seed population was proposed, and a seed filling chamber structure with lateral seed filling and free fall of the dragging seed was designed. The influence of the height of the seed layer and the structure of the seed filling chamber on the performance of the seed filling in the seed filling area of the seed-metering device and the solution of the dragging accumulation of the seed population were investigated by using the discrete element simulation. The simulation results showed that the average kinetic energy of the seed population inside the seed dispenser was increased with the increase of the filling seed layer height, and the average disturbance capacity of the seed population was gradually increased. Under the condition of 50mm seed filling layer height, the designed anti-drag strip accumulation seed filling chamber reduced the pressure on the seed population at the bottom of the seed filling area, and the phenomenon of population drag strip accumulation did not occur, and the disturbing effect on the seed population in the seed filling area was maintained. Seed metering tests were conducted on the JPS-12 seed-metering device inspection test bench, the test results showed that in the roller speed at 15~30r/min, suction seed negative pressure in the range of 1.0~1.2kPa seed-metering device qualified index could reach more than 90%. The results of the field test showed that the coefficient of variation of plant spacing stability was 4.4% and the coefficient of variation of seedling number consistency in each row was 8.14% in the actual field operation of the planter equipped with positive and negative pneumatic pressure combination roller-type small-size seed single-seed precision planter, which met the requirements of precision sowing.