To understand the effects of nitrogen deposition and precipitation changes and their interaction on soil organic carbon, an experiment was conducted in situ within the Rainy Area of Western China in an evergreen broad-leaved forest from November 2013 to December 2015. The study had six treatments: a control(CK), nitrogen deposition(N), water reduction(R), water addition(A), nitrogen deposition×water reduction(NR), and nitrogen deposition×water addition(NA). The results revealed that the soil organic carbon contents in the different soil layers were high in summer and fall, but low in spring and winter. The soil organic carbon content was higher in the 0-10 cm soil layer than in the 10-20 cm soil layer. The average soil organic carbon content followed the order: R < NR < CK < A < N < NA in the 0-10 cm soil layer and R < NR < A < CK < NA < N in the 10-20 cm soil layer. Simulated nitrogen deposition and water addition promoted soil organic carbon accumulation, but water reduction inhibited it. The soil C/N ratio for the 0-10 cm soil layer was significantly higher than for the 10-20 cm layer and showed a rising trend as soil depth increased. Water reduction reduced the soil C/N ratio, but water addition increased the ratio and soil total organic carbon (TOC) content. However, water reduction reduced the soil TOC content under the same simulated nitrogen deposition conditions. Simulated nitrogen deposition increased soil TOC under the same rainfall conditions. Furthermore, nitrogen deposition and precipitation changes had significant effects on the soil extractable dissolved organic carbon (DOC) and microbial biomass carbon (MBC) (P < 0.05) contents, but their effect on soil labile carbon (LC) was not significant (P > 0.05); and the interaction between nitrogen deposition and precipitation changes did not have a significant effect on the soil TOC, DOC, MBC, and LC contents (P > 0.05)