To improve nitrogen utilization efficiency in brown soil, in this paper, based on a soil cultivation experiment, the effects of two nitrification inhibitors and two organic materials on the inorganic nitrogen contents, N₂O and NH₃ emissions, and nitrogen conversion related enzyme activities and their mechanisms in brown soil were studied. Humic acid and biochar were used as exogenous organic materials, hydroxyphenylpropanoic acid (MHPP) and 3,4-dimethylpyrazole phosphate (DMPP) as biological sources and chemically synthesized nitrification inhibitors, respectively, and n-butylthiophosphate triamine (NBPT) as the urease inhibitor. Seven treatments 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 (UMNB). The results showed that inhibitors and organic materials improved soil physicochemical properties, affected soil nitrogen conversion related enzyme activities and nitrification and denitrification processes, further regulated soil NH₃ volatilization and N₂O emissions. 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 were significant differences in the total amounts 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 had a tendency reducing soil NH₃ volatilization loss. Soil N₂O emission was mainly affected by the NO- 3-N content. The DMPP group, which has a stronger nitrification inhibition effect, significantly reduced soil N₂O emissions due to lower soil NO- 3-N content, with a decrease of 44.83% to 70.87%, while the MHPP group had a decrease of 1.82% to 45.86%. In summary, the application of DMPP in brown soil in Northeast China can reduce the gaseous loss of nitrogen fertilizer in the form of N₂O, while the combined application of humic acid can reduce the total volatilization of soil NH₃, and their combination is more conducive to nitrogen sequestration in brown soil in Northeast China.