Depolymerization is a key process to control soil organic nitrogen mineralization and nitrogen availability supply. However, it is unclear that the affecting mechanism of nitrogen deposition on soil organic nitrogen depolymerization in subtropical forest. In this study, taking Pinus taiwanensis forest as the research object, a two-year nitrogen addition simulation experiment was set up by three levels including control (CT), low nitrogen (LN) and high nitrogen (HN) in Daiyun Mountain, Fujian Province. The mechanism of soil organic nitrogen depolymerization in response to nitrogen deposition was explored by analyzing the changes of soil chemical properties, microbial biomass and eight soil organic nitrogen depolymerizing enzyme activities. The results showed that short-term nitrogen addition significantly increased the content of mineral nitrogen in 0-10 cm and 10-20 cm soil layers, and significantly increased the content of microbial biomass carbon (MBC) in 10-20 cm soil layers. Simultaneously, the activity of Manganese Peroxidase in 0-10 cm soil layer increased significantly with nitrogen addition, and Laccase in HN was significantly higher than that of CT and LN. The activities of Acid Protease, Alkaline protease, Neutral protease and Laccase in 10-20 cm soil layer were increased significantly with the nitrogen addition, but the D-glutaminase activity was the opposite. Redundancy analysis showed that different influencing factors dominated the activities of organic nitrogen depolymerase in the two soil layers. Soil nitrate nitrogen (NO₃^--N) was the main influence factor of organic nitrogen depolymerase activities of 0-10 cm soil layer, while the organic nitrogen depolymerase activities of 10-20 cm soil layer was jointly affected by NO₃^--N and microbial biomass carbon (MBC) content. In conclusion, the responses of soil organic nitrogen depolymerization enzymes to nitrogen addition were inconsistent in subtropical Pinus taiwanensis forest soil, which were mainly regulated by soil NO₃^--N and MBC content. The mechanism of soil organic nitrogen depolymerization under nitrogen addition is very complex, and it will be an important direction in the future to study the process and mechanism of organic nitrogen depolymerization from the perspective of their polymerization effect. This study is helpful to broaden the response mechanism of soil nitrogen cycle to nitrogen deposition, and it has important implications for maintaining soil available nitrogen content and improving ecosystem productivity in Pinus taiwanensis forest.