The invention discloses a RS-485 communication system with priority double time control. The RS-485 communication system comprises an external interface protection circuit, a signal monitoring circuit, a signal priority control circuit, a power control circuit, a signal switching relay, a power switching relay and a RS-485 connection port. Data automatic acquisition based on a RS-485 bus is turnedfrom a traditional ''one master node multi-slave node'' topology into ''multi-master node multi-slave node'' topology to realize simultaneous access of a plurality of paths of RS-485 master nodes andslave nodes to the same RS-485 communication system, thereby improving the on-site wiring flexibility and convenience in automatic data acquisition of the RS-485 communication system.