Abstract: Through a long-term in situ simulated nitrogen (N) deposition experiment, we explored the response and mechanism of soil organic carbon (SOC) and total N content (TN) to exogenous N addition in warm-temperate Chinese pine (Pinus tabuliformis) forests. The levels of simulated N deposition were set as control (0 kg/(ha·a), N0), low N (50 kg/(ha·a), N1), medium N (100 kg/(ha·a), N2), and high N (150 kg/(ha·a), N3). Soil core method was used to investigate the responses of SOC and TN at different soil depths to simulated N deposition in the plantation and natural forests of P. tabuliformis. The results showed that SOC was reduced at different soil depths due to N deposition in both plantation and natural forests and the reduction of SOC was increased with N levels. Moreover, the SOC at surface layer (0-20 cm) declined more than that at deep layers (20-40 cm, 40-60 cm). Additionally, the SOC at surface layer in the natural forest declined more than that in the plantation. N deposition significantly increased soil TN at surface layer in the plantation (P0.05), however, the TN at surface layer in the natural forest was not significantly affected by simulated N deposition.