As an elemental carbon (C) and nitrogen (N) pool in the world, peatlands are very sensitive to environmental changes. Under global warming, the increase in available N affects the dynamic changes of plant community structure and nutrients in a permafrost peatland. This study was based on a long-term in situ N addition experiment that had been conducted for 9 years. It utilized the peatland in the permafrost area of Great Hing'an Mountain as the research object to analyze the effects of N addition on the growth characteristics, community structure, and nutrient dynamics of peatland plants. The N inputs were N1: 6 g N m−2·year−1, N2: 12 g N m−2·year−1 and N3: 24 g N m−2·year−1, respectively. Our results showed that the adding N can affect the plant community structure of peatland by affecting the plant growth characteristics. The diversity and richness of plant species in the peatland decreased as the concentration of added N increased. The long-term N addition can reduce the N limitation of plants to some extent. Still, it could further aggravate their phosphorus (P) limitation, resulting in the joint limitation of N and P or the complete limitation by P. The N resorption efficiency decreased with the increase of N addition level. The P resorption efficiency of different plants had varied responses to the changes in the N nutrient environment. Our study clarified the impact of long-term N addition on the plant community structure and nutrient dynamics of peatland in a permafrost area and provided an important theoretical basis to accurately evaluate the carbon and nitrogen balance of peatland in a permafrost area owing to future climate change.