Abstract: For the problems that the PLC controller failure in the gas drainage monitoring system makes the monitoring system unable to monitor and control the gas drainage system, a gas drainage monitoring system based on S7-1500R redundant PLC is designed. Through the redundant design of the CPU, power supply and RS485 interface of PLC, the hardware of PLC is configured and programmed, and the configuration software of upper computer is programmed. The unattended monitoring function of gas drainage system is realized, and the stability and reliability of gas drainage monitoring system are effectively improved. The field application shows that when one of the CPU, power supply, RS485 communication port, PROFINET cable and other components of S7-1500R redundant PLC fails, the system can automatically switch to the standby CPU, power supply and RS485 communication port to continue to work, and the gas drainage monitoring system can still monitor normally without affecting the normal operation of the gas drainage system.