Subtropical forest as one of the most typical forest ecosystems in China has rich species diversity of plants, animals and microorganisms. Global environmental changes can influence biodiversity and ecological function in the subtropical region. For example, atmospheric nitrogen (N) deposition profoundly affects the biodiversity, productivity and stability of forest ecosystems. Phosphorus (P) availability in subtropical forest soil is generally low, resulting in more exacerbated P limitation under N deposition scenarios. Soil microbes play key roles in organic matter decomposition and biogeochemical N and P cycling in soils and regulating forest succession. However, the effects of N and P inputs on forest soil characteristics at different succession stages remain largely unknown. A simulated N and/or P deposition experiments (10 g m^-2 a^-1, N addition (N), P addition (P), NP, and Control (without NP addition)) were conducted in a Chinese subtropical forest with two different succession stages (young forest < 40 and old forest > 85 a) since 2015. Soil samples were collected from three soil layers (0-15, 15-30, 30-60 cm) under four N and/or P addition treatments of two forest succession stages in June 2019. Soil microbial biomass carbon (MBC) and nitrogen (MBN), and soil nutrients content were determined through the CHCl₃ fumigation extraction and chemical analysis methods, respectively. The results indicated that soil MBC, MBN, and nutrients decreased with increasing soil depth regardless of the forest succession stages. Nitrogen addition had a minor effect on soil microbial biomass. Although no significant P addition effect was observed in the surface soil of young forest, P alone and NP additions significantly increased MBC and MBN in surface soil samples collected from the old forest (P<0.05), indicating that old forest would be more susceptible to P limitation than young forest. Soil dissolved organic nitrogen (DON), NH₄⁺-N, and NO₃^--N in the surface soils of the old and young forests were significantly increased under N addition conditions (P<0.05). Moreover, P and NP additions significantly increased available P (AP) in the surface and subsurface soils, and total P (TP) content in the surface soil of the two forest succession stages (P<0.05). Significant positive correlations between soil microbial biomass with soil nutrients were observed in this study. Soil total carbon (TC), total nitrogen (TN) and dissolved organic carbon (DOC) were identified as main factors influencing soil microbial biomass. This study provided basic data for revealing the response of forest soil qualities at different succession stages under future global environmental change scenarios.