Precision agriculture is the developing trend of modern agriculture, and the rational utilization of fertilizer is one of the key technologies in the precision agriculture, which needs to fertilize variably according to the crop needs and soil fertility conditions. Thus a fertilizer automated proportioning equipment is developed to Proportion the three fertilizers: Nitrogen fertilizer, Phosphorus fertilizer and Kalium fertilizer. The fertilizer will take greater effect after mixing sufficiently, so this paper mainly researched the mixing mechanism. The simulation and analysis of the velocity field and flow field of the fertilizer for the two paddles worked, the spiral-type paddle and multiple- fan-type paddle, are conducted respectively using Pro/E (Pro/Engineer) and CFD(Computational Fluid Dynamics) fluid dynamics analysis software. During simulation, the paddle models are meshed using the Gambit software. Then the multiple- fan-type paddle is determined to be the more suitable one through the FLUENT software.