Abstract: In order to improve pesticide efficiency, a variable spraying control system was designed with three working modes: a manual control, an automatic control and a calibration mode. The variable spraying control system took the S3C44B0X microprocessor of ARM7 series as its core control part and programmed with C language in the UCOS-Ⅱ environment. The system was able to fulfill the data acquisition and processing of the position and the speed about the sprayer, the pressure and the flow about nozzles, and recognize the plot and then adjust the electrical control valve to realize variable spraying. The test results in the field showed that the error of the variable spraying was less than 5% when the spray dosage was 465-600 kg/hm2 at speed of 4.2 km/h, the system can meet the requirements of variable spraying.