In order to explore the effect of biochar on nitrification and N₂O emission from water, the indoor incubation experiment was carried out after incorporating the pristine biochar (BC) or H₂O₂-modified rice husk-derived biochar (20% H₂O₂-BC and 30% H₂O₂-BC) combined with the screened heterotrophic nitrifying bacterium into the simulated wastewater. The dynamic changes of inorganic nitrogen contents, pH, bacterial amount, and N₂O emission of the incubation system were analyzed. Results showed that compared with BC, the amount of acidic oxygen-containing functional group of H₂O₂-modified biochars increased by 24.24%~26.98%, while the amount of alkaline oxygen-containing functional group, pH, and the specific capacitance significantly decreased by 22.16%~27.29%, 2.54~2.68, and 15.90%~30.94%, respectively. H₂O₂-modified biochars significantly inhibited nitrification driven by heterotrophic nitrifying bacterium compared with BC. Moreover, the 16-h cumulative N₂O emission of the treatments with 20% H₂O₂-BC or 30% H₂O₂-BC addition (0.0516 and 0.0525 μg N₂O/100 mL solution, respectively) were significantly higher than that with BC addition (0.0355 μg N₂O/100 mL solution). Correlation analysis showed that the cumulative N₂O emission of the treatments with 20% H₂O₂-BC or 30% H₂O₂-BC addition was significantly positively correlated with NH₂OH concentration in incubation system (r = 0.455 and 0.497, respectively), and showed no significant correlation relationship with NO₂^--N (p<0.05).