Continuous accumulation of nitrous oxide (N_2O) in the atmosphere leads to global warming and ozone depletion. Forest ecosystems act as source and sink of atmospheric N_2O, posing a great uncertainty in budgeting of atmospheric N_2O. Exogenous nitrogen inputs into terrestrial ecosystems are an alternative explanation for this uncertainty. Therefore, exploring mechanisms involved in responses of N_2O emission from forest soils to increased atmospheric nitrogen deposition is of some important theoretical and practical significance. However, due to complexity of soil nitrogen cycling and high spatial heterogeneity of forest ecosystems, progress of the research on soil N_2O flux response to N addition has been quite slow. N_2O emission in forest soils is mediated by microbial communities, and nitrification, denitrification, nitrifier denitrification and chemical denitrification are the four main processes of soil N_2O production. Presently, which one of nitrification and denitrificatiopn is the leading contributor to soil N_2O emission under nitrogen enrichment is still controversial; and how N_2O emission responds to increased N deposition and what mechanism is involved in soil microbes driving the porcess are not well known. In this paper, a review is presented of the progresses of the study on identification of sources of N_2O in forest soils using the stable isotope labelling technique, laws of the responses of total N transformation in and N_2O emission from forest soils to nitrogen addition, as well as effects of increased N depostion on activity and composition of soil microbial community. Also, the paper points out weak links in the present studies and possible research priorities in the future. Generally, soil N_2O flux is influenced by many environmental factors including soil temperature, soil moisture, pH, Eh, and N availability. Increased nitrogen deposition may increase, decrease or have little effect on forest soil N_2O emission, depending on forest types, initial nitrogen content in soils, and dose and duration of nitrogen application. Overall, the response of N_2O emission from forest soils to increased atmospheric N deposition exibits a nonlinear pattern, including no significant response at the early stage, linear increase at the medium stage, and exponential increase at the late stage. The three-stage pattern depends on degree of "N saturation" of the forest ecosystems. Besides, significant relationships were observed between soil NO_3~- content and abundance of denitrobacterial genes, between soil NH_4~+ content and abundance of nitrobacterial genes, and between soil N_2O flux and abundance of denitrobacterial genes. Nitrogen application leads to change in status of soil available N from N deficiency to N sufficiency, and hence changes in abundance and composition of nitrobacteria and dennitrobacteria, thus affectng soil N_2O emission. Moreover, as the monitoring of N_2O emission from forest soils and the researches on transformation of soil TN and dynanucs of N_2O producing bacterium communities are often carried out independently, making it hard to elaborate on the coupling relationship between soil microbial functional groups and soil N_2O emission.