An online mixing system was designed to improve the effective utilization of pesticides in spray operations. The pesticide mixing system mainly includes a water taking unit, a pesticide taking unit, a mixer and a control unit. When the system is working, the control unit controls the water extraction unit and the pesticide extraction unit to extract the required dose of the water and the pesticide into the mixer. The mixed liquid is pressurized by the diaphragm pump and sprayed by the nozzle. Based on the theory of computational fluid dynamics, a cylindrical static mixer model with 7 built-in spoilers was established for numerical simulation analysis. The pesticide injection ports and the water injection ports of static mixer vertically distributed along the side wall and the pesticide injection ports facing the first spoiler. The test results show that when the normal pressure of the pesticide is 0.1 MPa, the variation coefficient of the pesticide in the nozzle is 2.2%. At this time, the best mixing effect of the mixer is obtained, but there is a phenomenon of pesticide backflow in the injection port. Therefore, a simulation scheme is proposed for drug pressurization. Under the pressurized 1 MPa state, there is no reflux of the pesticide in the injection port, the variation coefficient of the pesticide mixture is 2.0%, and the mixer mixing effect is better than normal pressure. The carmine red solution was used to replace the pesticide, and the test was carried out by the ultraviolet spectrophotometry. The results showed that the maximum relative error of the mixed pesticide stability under pressure was 4.301%, and the variation coefficient of the pesticide was 3.989%.The mixing effect of the online mixing system under pressure is better than that under the normal pressure. The variation coefficient obtained by the test is basically consistent with the simulation results, and the online mixing system meets the design requirements. The diaphragm pump variable working condition test is carried out. When the ratio of the pesticide to water is varied from (1∶300) to (1∶3 000) with the water flow rate of 35-140 L/min, the mixing uniformity coefficient of the online mixing system is 4.670%.