[Objective] The mineralization processes of soil organic carbon under different water and nitrogen additions were studied to understand the relationship between the soil properties and carbon mineralization, and to provide scientific references for revealing the soil carbon conversion pattern in alpine steppe under global change.[Methods] A laboratory experiment was conducted with four different soil water contents (45%, 60%, 75%, 90% water-holding capacity, WHC) and four nitrogen levels (0, 0.2, 0.4, 0.8 mg/g). The following parameters were measured:CO₂ concentration, dissolved organic carbon (DOC), microbial biomass carbon (MBC) content, and enzyme activity.[Results] ①Within the experimented range of water and nitrogen addition, carbon mineralization volume showed a parabolic pattern. Soil carbon mineralization was more sensitive to the addition of water and the effect of the nitrogen addition on soil carbon mineralization was dependent on the water content. ②Increasing the water content from 45 to 60% WHC led to a faster leaching of the soluble substances from the soil, indicating a greater carbon mineralization. The soil organic carbon and microbial biomass carbon also showed an upward trend with an increase of the nitrogen addition from 0 to 0.4 mg/g. ③The soil carbon mineralization was inhibited either with the high WHC(90%) or by the addition of a higher content of nitrogen (0.8 mg/g) at 45% WHC. The high water content led to a lower soil carbon mineralization by a reduction in the soil porosity; whereas the addition of a high nitrogen content (0.8 mg/g) led to the inhibition of the soil carbon mineralization process by decreasing the availability of the DOC of the soil, level of MBC in the soil, and activity of soil microbial enzyme. The carbon mineralization inhibition by high-content nitrogen addition was alleviated at a high WHC(90%).[Conclusion] The predicted continuous increase in nitrogen deposition and precipitation in the Tibet Plateau may inhibit the carbon mineralization processes of the alpine steppes and benefit the accumulation of soil organic carbon.