In pneumatic precision metering device,positive and negative pressures are used to plant rapeseeds,but the trajectories of the seeds and the device′s performance are affected by the positive pressure.A high-speed photography technology was introduced to investigate the trajectories of rapeseeds with the rotating speed of 15 r/min and negative pressure of -1 500 Pa,and the positive pressures were set up from 50 to 600 Pa in the experiments.Target tracing technology was applied to capture the image of the rapeseed every 0.002 s in the dropping process and then a curve of the rapeseeds′ movement is formed on that base. The histogram of the rapeseeds′trajectories was analyzed and their distribution law was found through fitting Gaussian model.The relationship model between positive pressures and the dropping distances was developed.The velocities of rapeseed in the dropping process were introduced to analyze the motion states.The influence of seed spout was verified in the experiments.The results showed the trajectories were in norm distribution in every positive pressure,and the fitting curve between positive pressure and dropping distance was linear,and the correlation coefficient was 0.988,the average acceleration of rapeseed in different positive pressures were less than 9.8 m/s2 with the influence of air resistance;and it proved that the coefficient variance of trajectories was minimum during the positive pressures of 100-250 Pa.