In order to achieve the purpose of non-membrane advanced treatment of landfill leachate secondary effluent, a powerful electrochemical reaction unit is constructed with a composite cathode and a dimensionally stable anode (DSA) as the core. The composite cathode is synthesized from carbon felt and iron powder by magnetic adsorption. The composite cathode would precipitate iron-based coagulants and reduce nitrate nitrogen in the leachate. The anode is a Ti/RuO₂-IrO₂ electrode, which can activate Cl^- in the leachate to generate active chlorine and oxidize and remove ammonia nitrogen in the leachate. The powerful electrochemical reaction and ozone oxidation are applied in the same unit, and a powerful electrochemical-ozone coupling process is constructed to strengthen the removal of organic matter and total nitrogen in the secondary effluent of the leachate. The results show that when the current intensity is 1.5 A, the initial pH is 7, the adsorption density of iron powder is 0.42 g/cm², and the ozone dosage is 4.58 mg/min, the removal rate of COD is 46.46%, and the removal rate of TN is 81.70%. Through infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR), and cyclic voltammetry (CV), the reaction mechanism of the process for the removal of organics was explored. The results showed that ·OH and ·Cl were generated in the coupled process system. The organic compounds such as aliphatic compounds, esters, ethers, and phenols in the leachate were effectively removed, and the biodegradability of the leachate was improved. After the coupling process is combined with the small SBR biochemical system, the effluent meets the requirements of the Standards for Pollution Control of Domestic Waste Landfills (GB 16889—2008).