Abstract: The paper introduced a rapid determination technique of underground cable failure point.The technique firstly determines type of failure when optic transmission monitoring device starts to alarm, then uses methods of OTDR measurement, external line detection and fixed light source measurement successively to determine the fault location. Taking failure maintenance of underground monitoring network of Yangzhuang Coal Mine as an example, it illustrated specific determination process. Field application showed that the technique can accurately determine location of failure point, and provide accurate information for timely maintenance.