Abstract: In view of fact that current irrigation technology adopts timed artificial overall irrigation, water saving control cannot be carried out according to soil water content, and there is a problem of wasting water resources, based on internet of things and programmable logic controller（PLC）, a new intelligent water-saving irrigation system for farmland was designed．Optimization study was carried out in two parts．System hardware was mainly composed of a central processing unit, PLC module, radio frequency signal sensor, soil sensor, and temperature sensor．The PLC module inside system was mainly responsible for controlling water-saving irrigation structure．Signals collected on farmland monitoring terminal were stored in microprocessor to achieve conversion into a pulse signal that can be recognized by a computer system．The most suitable watering amount and timing were calculated by computer, CC2591 RF signal sensor was used to improve sensing speed, HL-TTN1 soil sensor was selected to detect soil water content, and PT100 sensor was used to detect temperature．Through the internet of things, grid processing was performed for land that needs to be irrigated, sensors were collected to test environmental parameters such as soil water content and air temperature, and Zigbee collaborative switch was used to set water-saving irrigation program．Experimental results showed that soil water content calculation error of farmland intelligent water-saving irrigation system based on internet of things and PLC could reach target value within 2%, which was efficient, high-quality water effects．