Abstract: With the increasing automation and intelligence of substations, wastewater discharge has gradually become characterized by small volume, intermittent flow, and considerable water-quality fluctuation. In cold regions such as Northeast China, low temperatures further constrain the stable operation of conventional biological treatment processes. To address this challenge, an electrocoagulation-electrooxidation-ultrafiltration/nanofiltration coupled process was developed and systematically evaluated for the removal of chemical oxygen demand (COD), suspended solids (SS), ammonia nitrogen (NH₃-N), and total phosphorus (TP), as well as for its operational stability, tolerance to water-quality fluctuation, applicability under intermittent operation, and energy consumption. The results showed that the optimal current density for both electrocoagulation and electrooxidation was 10 mA/cm2. Under optimized PAM and NaCl dosing conditions, the electrochemical units achieved effective removal of COD, SS, TP, and NH₃-N, with electrochemically treated effluent COD below 50 mg/L and NH₃-N below 5 mg/L, while TP and SS were reduced to very low levels. The subsequent dual-membrane unit provided further polishing, maintaining stable membrane flux over 120 h of continuous operation and reducing the final effluent COD to below 5 mg/L. Under high-pollution-load influent conditions, the coupled process still exhibited good effluent quality assurance and operational stability, indicating strong resistance to water-quality fluctuation. Intermittent operation tests further demonstrated its suitability for scenarios with small and discontinuous wastewater discharge. Under the optimized operating conditions, chlorinated disinfection by-products in the effluent remained at relatively low levels without obvious accumulation risk. The total energy consumption of the system was approximately 1.97 kWh/m³. Overall, the electrochemical-membrane coupled process is suitable for substation wastewater treatment in cold regions, especially for decentralized scenarios with strong water-quality fluctuation, and shows promising engineering applicability with pollutant reduction and potential carbon mitigation benefits.