Abstract: For the problem that communication network for power supply system of underground cannot meet real-time performance and reliability requirements of data transmission, and hardly achieves fast action and selectivity of protection simultaneously, the paper proposed a zone interlocking protection scheme based on switched Ethernet, and used OPNET network simulation software to study real-time performance of the switched Ethernet. The scheme adopts switched Ethernet of tree structure, and composes regional interlock system by adding smart interlock devices with Ethernet communication interface to integrated protection devices. The simulation results show that the maximum delay of overall network is less than 0.65 ms, the maximum end-to-end delay is less than 1 ms, and overall data transceiver flow is relatively smooth in the extreme case of 64 network nodes sending or receiving data at the same time, which illustrate that switched Ethernet has high stability and reliability to meet real-time requirements of interlock protection system in the region and prevent override trip accident.