Forest ecosystem, as the largest nitrogen storage pool on land, plays an important role in maintaining nitrogen biogeochemical cycle. In this study, three main plantation forests in China, namely Pinus Massoniana, Cunninghamia Lanceolate and Eucalyptus robusta, were selected as the research objects. The composition and distribution patterns of nitrogen reserves in different age groups and levels of three forest types were discussed. The results showed that:(1) With the change of stand age, the nitrogen storage of masson's pine, Cunninghamia lanceolata and Eucalyptus varied in 6.64-15.15 Mg/hm², 8.44-14.90 Mg/hm² and 3.22-11.29 Mg/hm², in which the nitrogen storage of Masson's pine, Cunninghamia lanceolata and eucalyptus reached the maximum in young forest, overripe forest and mature forest, respectively. Except for the young stage, the nitrogen reserves of Masson pine were the highest in the other stages of Chinese fir forest. (2) The ecological pattern of nitrogen storage in the three plantations was basically the same at each stand age. Most of the nitrogen was stored in the soil (0-100 cm). The nitrogen storage in the tree layer was next to that in the soil layer, and the nitrogen storage in the shrub layer was the smallest. In the range of 0-100 cm soil layer, each layer was divided by 10 cm, and the soil nitrogen storage in the surface layer of the three artificial forests was the highest at 0-10 cm of each age. The soil nitrogen storage in the soil layer of Masson's pine and Chinese fir increased gradually with the increase of stand age except for the young forest, and reached 10.71 Mg/hm² and 16.63 Mg/hm² in the overripe forest, respectively. In eucalyptus, nitrogen storage increased gradually from young forest to mature forest. Nitrogen storage in mature forest was 11.26 Mg/hm², but decreased in overmature forest. (3) There were differences in nitrogen storage of different organs at different levels in the same stand. The proportion of nitrogen storage in tree layer was the highest in the trunk of the three plantations, and the trunk was the main nitrogen pool in the tree layer. The middle layer of shrub layer had more nitrogen storage. Above ground part of herbaceous layer & GT; The underground part, the aboveground part is the main place of nitrogen storage; Fine root nitrogen storage 0-20 cm>20-40 cm. The nitrogen fixation capacity of different afforestation species was different. In general, the nitrogen fixation capacity of the ecosystem was gradually increased in the later stage of artificial afforestation, but decreased in the harvest stage of fast-growing eucalyptus plantation.