As an important part of aircraft power supply system, it is particularly important to realize cable fault online diagnosis and improve reliability. This paper designs a cable fault online detection and location device with the 500MHz board level rate based on FPGA by Spread Spectrum Time Domain Reflectometry (SSTDR), according to the characteristics of aircraft cable faults and the specification of aircraft cable detection. The instrument can realize the online detection and location of the open circuit, short circuit and intermittent arc of cables, and has the advantages of high positioning accuracy and good real-time performance. Using this device to monitor the health state of the cable fault on-line and realize the detection of the intermittent fault which is difficult to reappear, it can improve the efficiency of ground operation and afterwards maintenance to save a lot of manpower and material resources and has higher engineering value.