| In this study, we investigated the mechanism of organic contaminant removal in landfill concentrated leachate by ozonation technology, and the influence of reaction time, ozone dosage, initial COD concentration, initial pH and reaction temperature on removal efficiency. The reaction of humates in the leachate during the treatment process was studied using UV-visible and three-dimensional fluorescence spectroscopy. The study provides basic data and technological support for applying ozonation to treat humified wastes. The concentrated leachate for the experiment was brownish yellow, odorless, pH of 7.98, CODCr of 5492mg/L，BOD5/CODCr of 0.01, fluorescence index (f450/500) of 1.45, biogenic index (BIX) of 0.81 and humification index (HIX ) of 14.95. The treatment process of the leachate was A2/O + MBR + NF (RO) and treatment was carried out under different conditions by varying the following factors: reaction time (10, 30, 60, 90, 120, 180min); ozone dosing rates (0.67, 1.00, 1.33, 1.67g/h); initial COD concentration (undiluted leachate and diluted leachate with dilution factors of 1, 2, 4, 8), initial pH (3.01, 4.95, 6.99, 7.98, 8.5, 8.99, 9.99), and reaction temperature (27, 35, 38, 46℃) . The removal rate of COD and color were 37.6% and 58.0%, respectively, and the BOD/COD ratio increased from 0.01 to 0.39 when the system was operated under the most favorable conditions (reaction time, 90 min; ozone dosing rate, 1.67g/h; initial COD, 5492mg/L; initial pH, 7.98; reaction temperature, 27 °C). Increasing reaction time, ozone dosage and reaction temperature increased leachate degradation, while decreasing initial COD concentration and pH decreased reduction of humic substances. Furthermore, UV-Vis spectra analysis indicated that ozone treatment greatly decreased the degree of humification and aromatic compounds were effectively removed. Analysis of 3D-EEM spectra showed that ozone rapidly oxidizes the structurally stable fulvic acid-like organic matter in the leachate, transforming these substances to smaller, simpler structures that are more easily disposed of with further treatment.