Abstract: According to quantitative application mode of existing farmland spraying machine in China, a set of variable application system based on fuzzy PI control was designed．The system used multi-sensors to collect parameters such as speed, flow rate and pressure of sprayer in real time, and took this as control basis, liquid flow in pipeline was adjusted in real time by changing opening of proportional valve, and controled opening and closing of several groups of nozzles at the same time．The system adopted flow regulation scheme of main road, and five groups of switching solenoid valves control multiple groups of sprinklers．The flow control test and field spraying test of sprayer nozzle were carried out．Results showed that flow error of a single sprinkler was less than 2.5%, fuzzy PI control was better than traditional PI control, and field spray error was less than 2.2%．