Abstract: To investigate how tropical rainforest restoration influences the spatiotemporal dynamics of soil nitrogen accumulation and partitioning, we selected three representative communities in Xishuangbanna that span successive restoration stages: Mallotus paniculatus (early stage), Mellettia leptobotry (mid-stage), and Syzygium oblatum (late stage). Using standard soil chemical analyses, we quantified total nitrogen (TN), hydrolysable nitrogen (HN), ammonium-nitrogen (NH₄⁺-N) and nitrate-nitrogen (NO₃⁻-N), along with their allocation ratios (HN/TN, NH₄⁺-N/TN, \mathrmNO_3^ - _3^ + -N/TN). The effects of vegetation diversity and soil physicochemical properties on soil nitrogen accumulation and allocation were also analyzed. The results showed that all nitrogen fractions increased significantly with restoration progression (p < 0.05), relative to the early stage, hydrolysable nitrogen and ammonium nitrogen in the late stage rose by 70.2% and 64.2%, respectively. Nitrogen fractions and their allocation exhibited significant monthly and depth-related variations, peaking in June and decreasing with increasing soil depth. Meanwhile, restoration markedly enhanced plant diversity and soil nutrient accumulation, the Shannon diversity indices of both the tree layer and the understory were 1.43-fold and 1.55-fold higher, respectively, at the late stage than at the early stage. Structural equation modeling further revealed that plant diversity, soil temperature, total organic carbon, and microbial biomass carbon were the dominant controlling factors regulating soil nitrogen dynamics, jointly explaining 82% ~ 94% of the variation in nitrogen fractions and 28% ~ 52% of the variation in their allocation. Therefore tropical forest restoration, through reshaping plant diversity, microclimate, and soil carbon pools, significantly promotes the accumulation and redistribution of soil nitrogen fractions. This study provides new empirical evidence for unraveling the mechanisms of soil-nitrogen cycling under tropical rainforest restoration.