Abstract: 【Objective】Increased atmospheric nitrogen deposition has significantly altered the pathway and quantity of nitrogen input to the terrestrial ecosystems, and consequently influenced the ecosystem function. The atmospheric nitrogen deposition in future was emulated through applying inorganic nitrogen to the forest floor. The effect of nitrogen addition on the soil nitrogen transformation and the greenhouse gas emission was then investigated, the results of which could help evaluated the role of the forest ecosystems in northern China in coping with the global change.【Method】Inorganic nitrogen in the form of ammonium nitrate(NH₄NO₃), was scattered evenly on the floor of a Pinus tabulaeformis forest under rates of 0, 5, 10, 20 and 40 g/m² with four replications, for a total of 20 plots. In August 2017, soil cores were sampled for the monitoring of total nitrogen(TN), total soluble nitrogen(TDN), ammonium nitrogen(NH⁺₄-N), and nitrate nitrogen(NO^-₃-N)contents. Then, soil greenhouse gases(N₂O, CO₂ and CH₄)were collected using the static chamber method to assess the effects of nitrogen addition on soil nitrogen and greenhouse gas emissions.【Result】Inorganic nitrogen addition significantly increased NO^-₃-N content by 25.04%-246.4%, TDN content by 13.29%-73.82%, and soluble organic nitrogen(DON)content by 4.54%-70.51% in the top 10 cm of the soils. Higher nitrogen treatment gradients significantly increased soil NH⁺₄-N concentrations. No obvious variation was monitored by simulating nitrogen deposition. Nitrate nitrogen and TDN contents were markedly increased in N10, N20 and N40 plots(P < 0.05). DON concentration was significantly increased by N40 treatment. Simulated nitrogen deposition significantly affected soil nitrogen fractions at the soil depth of 0-10 cm. In the ≥10-20 cm soil layer, there was a trend for higher TN and NH⁺₄-N concentrations across nitrogen plots. The content of NO^-₃-N was significantly increased by 234%, 284% and 663% by N10, N20 and N40 treatments, respectively. The concentration of TDN increased with higher nitrogen treatment levels. However, nitrogen deposition significantly decreased soil DON concentration. The greenhouse gases N₂O and CO₂ were positively correlated with inorganic nitrogen addition, with significant increases found in the N20 and N40 treatments(P < 0.05). In addition, nitrogen addition significantly decreased soil CH₄ assimilation, as more CH₄ was emitted at higher levels of nitrogen addition. Correlation analyses suggested that the concentration of NO^-₃-N was significantly correlated with variation in DON, N₂O and CO₂ concentrations(P < 0.05). The concentration of DON was negative correlated to N₂O, CO₂ and CH₄. Although positive trends were discovered between NH⁺₄-N and TDN with N₂O, CO₂ and CH₄, these correlations were not significant.【Conclusion】Inorganic nitrogen addition considerably increased the available nitrogen content in the soil and the emission rates of greenhouse gases, especially under N20 and N40 gradients. The increased available nitrogen concentrations in the soil significantly accelerated forest soil greenhouse gas emissions. Overall, simulated atmospheric nitrogen deposition significantly altered forest soil nitrogen transformation and greenhouse gas emissions.