Soil salinization has become a global issue. Saline and alkaline arable land was taken as research object in this paper and four salt gradients were set (S1: 0.1%; S2: 0.5%; S3: 0.9%; and S4: 1.3%). Through the addition of different substrates (CK: no addition of substrate; N: addition of nitrogen source; C: addition of glucose, C+N: addition of glucose and nitrogen source) to soil, it analyzed the influence of salt content on the soil microbial biomass carbon (SMBC) for the purpose of surveying the response mechanism of soil carbon turnover to salt stress. Results indicated that after addition of different substrates, the SMBC in high salt content (S3 and S4) is obviously lower than that in low salt content (S1 and S2). The decline rate of S3 and S4 is 5.4% and 14.2% for no addition of substrate; the decline rate is 9.0% and 24.0% for addition of nitrogen source; the decline rate is 11.5% and 28.0% for addition of carbon source; the decline rate is 19.5% and 39.5% for addition of carbon source + nitrogen source. Compared with no addition of substrates, addition of nitrogen source could not increase the SMBC. Addition of carbon source and carbon + nitrogen can significantly increase the SMBC, and the increase in low salt content soil (80.0%-81.0% and 58.0%-59.0%) is obviously higher than high salt content soil (52.0%-69.0% and 34.0%-50.0%). Generally, when the soil salt content is low (0.5%), the influence of different substrate treatment is little on the SMBC, and increasing the soil salt content can obviously reduce the SMBC.