Fault detection of railroad signal cable is of great significance to the safe operation of railroad system. For the most common high-resistance fault problem of railroad signal cable, the inhomogeneous characteristics of railroad signal cable structure are analyzed by measuring the electrical parameters of several 1 m cables, and the normal model of cable inhomogeneous parameters is constructed, and finally the inhomogeneous high-resistance fault simulation model of railroad signal cable is established. The feasibility of the Frequency-domain reflection (FDR) method in locating high resistance faults in railroad signal cables is verified. And a hardware system is designed independently based on the FDR method, which transmits a 0.1~5 MHz sweep signal to the cable and collects the echo signal required by the FDR method through the intermediate frequency detector, and then subsequently carries out the data processing in the upper computer to realize the localization of high-resistance faults of 0.1 MΩ and 0.5 MΩ within 1000 m. The actual localization effect of the FDR method in detecting high resistance faults in railroad signal cables is verified.