The major function of anti grade trip of underground coal mine power supply system is making the distributing point nearest from the fault point trip. However, singlebus connection is employed among every distributing points which makes the anti grade trip a complicated twostage communication network and will hardly meet the realtime requirement. The underground anti grade trip program is proposed based on the idea of substationarea protection, this program is implemented by a singlestage communication network which is composed of a RTEthernet constituted by substationarea protection device and monitoring host. The main function of substationarea protection device includes collecting electric information of distributing points from underground power supply system and confirming malfunction and upload malfunction information. The monitoring host locates the distributing point where the malfunctioning circuit lies by fault matrix method then sends a tripping order to the substationarea protection device to impel the breaker nearest from the fault point to trip. Meanwhile the realtime property of the anti grade trip system is guaranteed by the application of high performance RTEthernet. Experimental results show that this program can make the breaker nearest from the fault point trip, and in the mean time meets the real time requirements of the underground anti grade trip, thus providing a new solution to the coal mine grade tripping.