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In order to meet the requirement of top dressing in the middle and late period of maize growth, a kind of pneumatic gathering and discharging type corn precision fertilizer mixing device was designed. The variable mixing fertilizer scheme with pneumatic set and row was designed. The motor driven blade rotation was used to mix fertilizer, and the inside of the fertilizer distributor was designed as a cone structure. By means of computer fluid dynamics, discrete element coupling method and two factors and five levels orthogonal experiment, the dip angle of the fertilizer outlet and the structure and arrangement of the bellows at the upper end of the distributor were studied. With the coefficient of variation of fertilizer discharge in each row as the test index, and with the angle of fertilizer discharge outlet, conveying gas velocity, and bellows length as the experiment factors, a three-way quadratic regression orthogonal combination design experiment was conducted to obtain the optimal operation parameters of key components of the precision fertilizer mixing device, namely, the angle of fertilizer discharge outlet of 45°, conveying gas velocity of 35m/s, and bellows length of 568mm. The inlet layout of fertilizer mixer was as follows: central layout, and the number of blades was 8. In June 2019, the machine field inspection was done at the National Agricultural Machinery and Tools Quality Supervision and Inspection Center, the inspection results showed that the machine's fertilizer application error was 2%, the total fertilizer application stability coefficient was 2%, and the fertilization rate was less than 2%. The research result can provide useful reference for the design and development of pneumatic fertilizing machinery and tools.