Abstract: In order to realize the efficient automatic control of farmland water-saving irrigation, with Siemens S7-200 PLC as the core, combined with Siemens MM440 inverter, water pump motor, sensor, EM235 analog module and other hardware equipment to design a farmland water-saving irrigation automatic control system. Detailed analysis of the hardware and software design elements of the system. The system can sample irrigation water pressure and water level data through sensors, use PID algorithm to analyze the data, and feed it back to PLC for adjustment to achieve closed-loop control of constant pressure irrigation to achieve the effect of automatic water saving.