The safe operation of railway signal cables is critical to the railway system. Addressing the issue of multiple reflection interference caused by port impedance mismatch in traditional Frequency Domain Reflectometry (FDR) during high-resistance fault detection, this paper establishes a signal reflection model for faulty transmission lines to investigate secondary reflections induced by source mismatch and the impact of various matching strategies. Furthermore, a programmable impedance matching FDR detection system based on a discrete LC network is designed, achieving flexible source impedance reconstruction within the 0.1–5 MHz frequency band. On this basis, a 1000 m cascaded cable experimental platform is constructed to compare the fault location performance of three strategies: no matching, conjugate input impedance matching, and cable local characteristic impedance matching. The results verify the improvement provided by impedance matching on the anti-interference capability in the detection of high-resistance faults in railway signal cables.