As a strong oxidant, ozone is often used as a bactericidal disinfectant for MBBR systems. In order to obtain the effect of ozone on the water quality of MBBR treatment and on the bactericidal rate of Vibrio parahaemolyticus, a 10 L reactor was used to determine the nitrification capacity of the system and the number of viable dead cells of the biofilm samples under a 10 L reactor at 60% filling rate to study the effects of different concentrations of ozone (0、1、2、4、6 mg/L) on the nitrification capacity of the system and the killing of Vibrio parahaemolyticus. The results showed that 2 mg/L ozone had no significant effect on cell mortality in biofilm sample (P = 0.49). The removal rates of TAN were 55.11% ± 5.32%, 57.89% ± 9.01%, 49.2% ± 5.99%, 33.07% ± 2.68%, 34.22% ± 8.89%, and the 4 mg/L ozone dose group was significantly lower than that of 0、1、2 mg/L ozone dose group (P = 0.042). At ozone doses above 2 mg/L, Vibrio parahaemolyticus was not detected on TCBS plates. This study showed that according to the mortality rate of biofilm cells, the treatment efficiency of ammonia nitrogen and the sterilization rate of Vibrio parahaemolyticus. The 2 mg/L ozone can effectively kill Vibrio parahaemolyticus and do not affect the nitration reaction efficiency of MBBR.