In this paper, the optical communication networks applied in Power States are introduced. The present methods for EPON fiber cables monitoring are analyzed and evaluated. A new method which is composed of OTDR(Optical Time Domain Reflectometer), light switch, and optical multiplexer reflector(final filter) is proposed for fiber optic online monitoring. The on-line monitoring system can monitor the real-time transmission of fiber-optic cables, detect hidden obstacles and quickly position the fiber obstacle. Implementation of the parallel monitoring system will improve the time of barriers clearing, and lower the fault probability of Optic fiber communications in Power States.