Studies on CO₂ fluxes from boreal forest soils and their control factors under increased atmospheric nitrogen (N) deposition are essential. In this study, a manipulative N addition experiment was created in a boreal forest in the Daxing’anling region to investigate this. Soil CO₂ fluxes were measured by the static chamber–gas chromatography method and soil temperature, soil moisture, soil inorganic N and dissolved carbon content (DOC) were simultaneously measured to explore the main factors affecting CO₂ emission from the soil. Results showed that N addition did not significantly change soil moisture content. Nitrogen addition significantly reduced soil dissolved inorganic carbon (DIC) content in the organic layer and increased soil DOC in the organic and mineral soil layers. Short-term N addition did not increase soil NH₄⁺-N content, but significantly increased soil NO₃^--N content. Exogenous N input tended to increase CO₂ emission from the coniferous forest soil. Soil CO₂ flux was mainly driven by soil temperature, followed by soil moisture and DIC content. The overall pattern of soil CO₂ fluxes was dominated by soil temperature but soil moisture appeared to control variation during peak growth periods. These results show that when investigating effects of N addition on soil CO₂ flux, the roles of soil available N and C dynamics should be considered as well as soil temperature and soil moisture.