Fault detection of railroad signal cables is of great significance for ensuring the safe operation of railroad systems. To address the most common high-resistance fault problem in railroad signal cables, the inhomogeneous characteristics of cable structures are analyzed by measuring the electrical parameters of multiple 1 m cable segments. Based on these measurements, a normal model of inhomogeneous cable parameters is constructed, followed by the establishment of an inhomogeneous high-resistance fault simulation model for railroad signal cables. The feasibility of the frequency-domain reflectometry (FDR) method for locating high-resistance faults in railroad signal cables is then verified. Furthermore, a dedicated hardware system based on the FDR method is independently designed. This system transmits a 0.1 MHz to 5 MHz swept-frequency signal into the cable and collects the reflected signals required for FDR analysis through an intermediate-frequency detector. The collected data are subsequently processed on a host computer to realize the localization of high-resistance faults with resistance values of 0.1 MΩ and 0.5 MΩ within a cable length of 1000 m. Experimental results confirm the effectiveness and accuracy of the FDR method for detecting and locating high-resistance faults in railroad signal cables.