Abstract: The PLC/DCS real-time monitoring and control of the terminal actuator in the traditional process control system leads to heavy system resource consumption, and the failure of a single of equipment is easy to cause communication breakdown of the whole system and other industrial problems. To enhance the communication fault-tolerant ability of the system and make PLC and terminal actuators connect stably and reliably, a dual-loop redundant bus controller based on Modbus was designed and implemented. The controller adopted dual CPU and the design of redundant heat backup, which effectively reduced the PLC workload, improved the system robustness and real-time performance, and was suitable for industrial field.