Abstract: Aiming at the problem of low precision of blade fertilizer spraying flow control of four rotor UAV, a four rotor UAV blade fertilizer control system based on Fuzzy PID control is designed.In this design, the electromagnetic flow regulating valve of four rotor UAV is taken as the research object, the mathematical model of the electromagnetic flow regulating valve is established, and the opening of the electromagnetic valve is controlled by the combination of fuzzy control and PID control; Compared with conventional PID control, Matlab/Simulink is used to verify the accuracy of foliar fertilizer spraying model and the effectiveness of control system; A four rotor UAV foliar fertilizer spraying control platform is built, and the spraying effect test is carried out to verify the control accuracy and effectiveness of the fuzzy PID control algorithm.The simulation results show that the fuzzy PID control curve is more in line with the change law of the target curve than the conventional PID control curve. For the electromagnetic flow valve control, the fuzzy PID control performance is better than the conventional PID control.The test results show that the maximum error between the actual flow and the theoretical flow under different flight speeds is not more than 2.50%, which meets the requirements of spraying operation.