Abstract: Precision agriculture is the development direction of agricultural production. According to the development needs of the variable spray technology in precision agriculture, the variable spray technology is studied. This paper mainly introduces a variable spray system based on Programmable Logic Controller（PLC） to verify the variable performance through the test. The variable spray system is mainly composed of PLC, touch screen（Touch Panel Monitor）, solenoid valve, drug water pump, pressure gauge and power supply module. The system uses the touch screen to send the variable signal to the PLC through the RS232 communication. After receiving the signal, the PLC adjusts the opening degree of the solenoid valve to achieve the purpose of the variable spray. Establish the model parameters of line pressure, solenoid valve opening and head spray amount through the tests of solenoid valve opening. The test results show that the spray system has a good variable power of 6.77 under the same pressure and 9.91 under different pressure and different opening operating conditions. The function between the solenoid valve opening and the spray amount is analyzed and verified at different pressures. The curve fitting results show that by using the linear function, index function and polynomial function, the determination coefficient is greater than 0.9, where the maximum is 0.9998. The relative error analysis results show that the average relative error of the exponential function and the polynomial function fitting is within 4%, which provides technical and data support for the design and application of the variable sprayer.