3.0%以内。This paper developed a mixing pesticide device, a differential pressure flow meter, and a flow metering valve, with the corresponding control system, to achieve variable rate spraying based on online mixing pesticide. Variable rate spraying was implemented by using the system to measure flow of water and pesticide, and control chemical flow in real time. The experimental results show that the errors of the flow meter are within ±2.0%, and the controlling errors of chemical flow are within ±3.0% in this system.