Abstract: Objective Traditional equipment used for electrical fire leakage insulation monitoring in metro systems suffers from low leakage detection accuracy, poor traceability, and high false alarm rates. To address these issues, it is necessary to develop a novel resistive leakage insulation detector. Method Beginning with the current state of metro leakage monitoring, false alarm phenomena and their causes in existing detection equipment during application are analyzed. Based on the characteristics of electric current, a separation and extraction method for resistive hazard causing components is designed. The detection principle, hardware composition, and software logic of resistive leakage insulation detector are elaborated. Throughout the leakage insulation monitoring process, the fundamental wave residual current serves as the benchmark to ensure signals remain unaffected by higher harmonics, thereby enhancing the data processing accuracy. A test distribution cabinet is constructed to conduct monitoring effectiveness verification trials. Using traditional residual current detectors as the baseline, the monitoring performance of the resistive leakage insulation detector is validated. A metro line station in Beijing is selected as a pilot site for equipment application testing. Result ＆ Conclusion The resistive leakage insulation detector based on fundamental wave residual current can ensure signal immunity to higher harmonic interference, and improve equipment data processing accuracy. Verification test results demonstrate that the reduction of resistive leakage insulation detector false alarm rate correlates with line capacitive inherent leakage current. When resistive leakage current is less than capacitive inherent leakage current, the false alarm rate decreases by over 95 %. Field validation in low-voltage switchgear environments at the pilot site confirms that compared to traditional residual current detectors, the resistive leakage insulation detector reduces the false alarms of electrical fire current leakage by 98.9%, significantly enhancing electrical fire monitoring capabilities.