Abstract: The integrated ozone-biological aerated filter (BAF) is a potential energy-saving process for advanced treatment of industrial wastewater treatment by ozonation. However, there were few reports on the influences of the ozonation technology on the treatment effects of integrated ozone-BAF. The treatment effect of integrated ozone-BAF process on the biochemical effluent of petrochemical wastewater was studied under three kinds of ozonation methods: ozone alone, ozone/H₂O₂ and ozone/catalyst. Molecular weight distribution of effluent organic matter, three-dimensional fluorescence regional integration change, BAF microbial morphology, biomass and biological activity were helped to explore the removal characteristics of organic matter. The results showed that the average chemical oxygen demand (COD) was 55.7 mg/L at the optimal ozone dosage of 5 mg/L in single ozone-BAF technology. COD accumulated to a certain extent by the ozone/H₂O₂-BAF technology. The average COD achieved to 39.5 mg/L (removal rate was 39.9%) at the optimal ozone dosage of 5 mg/L in ozone/catalyst-BAF technology, and effluent COD could meet Emission Standard of Pollutants for Petroleum Chemistry Industry (GB 31571-2015) stably. In single ozone-BAF technology, organics with molecular weight ≤1 300 Da and 3 000-6 000 Da increased, the biomass decreased by 68.3%. In ozone/H₂O₂-BAF technology, organics with molecular weight ≤800 Da increased, and the biomass decreased by over 60.0%. In the ozone/catalyst-BAF technology, almost the organics with whole range of molecular weight were removed, the biomass reduced by 48.3%, and the bioactivity increased by 106.4%. Soluble microbial by-products and humic acids were removed significantly by the ozone/catalyst-BAF technology.