Abstract: Combining with the principle of fiber channel structure and operation, the problem of channel alarm is analyzed in ultra-high voltage power grid, for both dedicated fiber channel and multiplexed channel. Based on the actual situation of operation and maintenance, a troubleshooting and locating method of channel fault under different alarm symptoms is summarized in this paper, and the validity of the method is verified by resolving a practical case. Finally, some suggestions for the operation and maintenance management of 500 kV line protection channel are put forward.