Abstract: As an important parameter of O₃/BAC, ozone dosage directly affects the purification effect of water and operation costs. The optimal pre-ozone dosage and optimal post-ozone dosage were determined based on the removal efficiency of general pollution indices (e.g., COD_Mn, UV₂₅₄ and turbidity) in ozone-activated carbon, which are pre-ozone/BAC (process Ⅰ) and post-ozone/BAC(process Ⅱ). The study also compared the removal efficiency of organic pollutants, before and after ozonation, in the process Ⅰ and process Ⅱ. The results showed that the optimal pre-ozone dosage was 0.78mg/L in process Ⅰ, while the removal efficiencies of COD_Mn and UV₂₅₄ at the optimal pre-ozone dosage were 28.9%, 43.7% respectively higher than those at zero; the optimal post-ozone dosage was 1.20mg/L in process Ⅱ, and the removal efficiencies of COD_Mn and UV₂₅₄ at the optimal post-ozone dosage were 44.8% and 73.7% respectively higher than those at zero. It could be seen that, when O₃/BAC process was used for Danjiangkou Reservoir water advanced treatment, it could effectively remove the organics and comprehensively improve the water quality in the optimal ozone dosage. Moreover, the treatment capacity of process Ⅱ was better than that of process Ⅰ after the water treatment for the Danjiangkou Reservoir.