Combining the need of power cable fault online location in power system with the technical advantages of optical fiber sensor, this paper proposes a set of power cable fault online location system with the characteristics of optical time domain reflection location mechanism of the optical fiber sensor, and it presents the use of power cable fault in the on-line location system. The design of laser emission circuit, photoelectric detection circuit design, GPRS communication circuit design, the design of the system software structure are also described in detail. The system overcomes disadvantages that power outage measurement and repair time is too long in traditional location methods.The field test results show that the system has high accuracy and high reliability.