Abstract: The fault of under-grounding power supply system often causes override-tripping. The problem has seriously affected the safety of underground production and security of mine workers. This paper proposed a kind of cascaded fiber longitudinal differential protection which is based on distributed intelligent protection principle. The action principle of the protection was stratified and dispersed which would improve the safety and reliability of underground power supply system. The practical application proves that this method can effectively prevent override tripping and reduce the occurrence of the underground blackout accidents thus ensuring ensure the safe operation of underground power supply system.