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In view of the lack of cotton field fertilization combined soil preparation machinery and the low control precision of fertilizer application in Xinjiang, a variable fertilization combined soil preparation machine was designed, which could complete the operations of harrowing, variable fertilization, soil leveling, soil crushing and suppression at one time. The key components such as fertilizer discharge device, double disc trenching mechanism, notch rake group, soil crushing and pressing components were designed. The key factors affecting its working performance were obtained through static analysis, and the structural parameters of key components were determined. Based on the Beidou automatic navigation driving system, the driving speed was obtained, and the variable fertilization control was realized with STM32F405 as the core processor. The field experiment was carried out with the consistency of fertilizer amount in each row, the control accuracy of fertilizer amount at different driving speeds and the qualified rate of fertilization depth as the evaluation indexes of fertilization performance, and the stability of rake depth, standard deviation of surface flatness and rate of broken soil as the evaluation indexes of soil preparation performance. The test results showed that when the rotation speed of the fertilizer shaft was 10~60r/min, the maximum coefficient of variation of the consistency of each row of fertilizer was 4.27%. When the driving speed was 4km/h, 7km/h and 10km/h, the minimum control precision of fertilizer discharge was 96.70%, 95.35% and 94.14%, respectively. The qualified rate of fertilization depth was 87.04%. The maximum coefficient of variation of rake depth stability was 5.34%. The maximum standard deviation of surface roughness was 4.69mm. The broken soil rate was 96.16%. All indexes met the requirements of fertilization machinery and soil preparation machinery standards.