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According to the working principles of the air-suction precision seeder, the 3-D model of seeds pickup process was established. Take the compressibility and the viscosity of the real gas into account, the N-S equations and standard k-ε turbulence model were applied to calculate the forces on seeds in the gas field nearby the vacuum nozzle by using the computational fluid dynamics (CFD) software Fluent. The axial pickup distance, the radial pickup distance, the volume of effective pickup region and the seeds pickup tracks were received through the binary linear interpolation method. The effects of the diameter of nozzles and the differential pressure on the pickup performance were analyzed, the results showed that the pickup performance of conical nozzle was better than the straight nozzle and the bore hole and it would be improved with the increasing of nozzle diameter and the differential pressure. The rape seeds were selected as experimental material, the optimum parameters combined with conical nozzle of Ф1 mm, the roller's rotational speed of 14 r/min. and the differential pressure of 2 kPa were received through orthogonal tests. The parameters were tested to be the best with the seeds single pickup ratio of 92%, the seeds missing pickup ratio of 4% and the seeds multiple pickup ratio of 4%.