To investigate the effects and mechanisms of different nitrification inhibitors combined with exogenous organic materials (humic acid, biochar) on nitrogen transformation and NH3 and N2O emissions in Northeast brown soil, and to provide theoretical support for improving nitrogen utilization efficiency in brown soil. Based on a soil cultivation experiment, the effects of two nitrification inhibitors and organic materials on the inorganic nitrogen [ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N)] content, N2O and NH3 emissions, and nitrogen conversion related enzyme activity in brown soil were studied. The exogenous organic materials used are humic acid and biochar. Hydroxyphenylpropanoic acid (MHPP) and 3,4-dimethylpyrazole phosphate (DMPP) represent biological sources and chemically synthesized nitrification inhibitors, respectively. The urease inhibitor selected is n-butylthiophosphate triamine (NBPT). Seven processes were set up, including urea (U); Urea + DMPP + NBPT (UDN); Urea + MHPP + NBPT (UMN); Urea + DMPP + NBPT + humic acid (UDNH); Urea + MHPP + NBPT + humic acid (UMNH); Urea + DMPP + NBPT + Biochar (UDNB); Urea + MHPP + NBPT + Biochar (UDNB). The results showed that inhibitors and organic materials can improve soil physicochemical properties, affect soil nitrogen conversion related enzyme activity and nitrification and denitrification processes, further regulate soil NH3 volatilization and N2O emissions. The nitrification inhibition rate reflects the degree of inhibition of soil ammonium oxidation process. Compared to U, the peak net nitrification inhibition rate of the DMPP group reached 72.40% to 89.04%, which was higher than that of the MHPP group (9.63% to 33.00%). There was a significant difference in the total amount of NH3 volatilization among different fertilization treatments, with the order of UDNB>UMNB>UDN>UDNH>UMN>UMNH>U. Compared with U, the addition of biochar significantly increased soil NH3 volatilization by 496.9% to 579.7%. On the contrary, humic acid has a tendency to reduce soil NH3 volatilization loss. The soil N2O emissions were mainly affected by the NO3--N content. The DMPP group, which has a stronger nitrification inhibition effect, significantly reduces soil N2O emissions due to lower soil NO3--N content, with a decrease of 44.83% to 70.87%, while the MHPP group has a decrease of 1.82% to 45.86%. In summary, the application of DMPP in brown soil in Northeast China reduced the gaseous loss of nitrogen fertilizer in the form of N2O, while the combined application of humic acid reduced the total volatilization of soil NH3. The combination of the two is more conducive to nitrogen sequestration in brown soil in Northeast China.