Abstract: As a kind of high concentration organic wastewater, the wet stacking wastewater from the edible mushroom breeding is hard to be degraded with dense COD and ammonia nitrogen. It poses a challenge to make the discharge reach the standard just using conventional treatment processes.The combined process of Air Floatation-Baffled A/O Biofilm Reactor (HAOBR)-O₃/H₂O₂ was adopted to study the treatment effect of Air Floatation-HAOBR on COD and ammonia nitrogen in mushroom breeding wastewater, to discuss the treatment effect and optimal control parameters of O₃/H₂O₂ catalytic oxidation section under different combination modes. Three-dimensional fluorescence spectroscopy was employed to analyze the variation of dissolved organic matter (DOM) in the wastewater in this combined process. The results showed that the concentration of COD and ammonia nitrogen in the mushroom wastewater decreased to (485±25) and (1.32±0.11) mg/L respectively after the treatment of Air Flotation-HAOBR; when the dosage of O₃ and H₂O₂ was 0.88 and 333 mg/L respectively; the final effluent COD and ammonia nitrogen concentrations were (22.50±1.50) and (1.30±0.15) mg/L respectively, and the average removal rates were 99.40% and 98.70% respectively. It was assayed that fulvic acid-like substances, soluble microbial metabolites and humic acid-like substances were the dominant DOMs in mushroom breeding wastewater. After the treatment, the fluorescence intensity of DOM was greatly reduced, but the major components remained unchanged. The combined process could effectively remove COD, ammonia nitrogen and DOM in mushroom breeding wastewater, and the effluent could meet the first level discharge standard of Integrated Wastewater Discharge Standard (GB 8978-1996), with a good prospect for the treatment of mushroom breeding wastewater.