Forest fire significantly affects soil carbon sequestration capacity and components of soil organic carbon content by changing soil physicochemical properties. Explaining the effects of different fire severities on soil organic carbon of Pinus yunnanensis forest is of great significance for ecosystem restoration and soil carbon pool management of Pinus yunnanensis forest after fire. In this study, the soils of Pinus yunnanensis after 2 years fire in different soil layers (0-5, 5-10, 10-15, and 15-20 cm) in Lushan Forest Farm, Sichuan Province were taken as the research object. According to different fire severities (unburned, low severity, moderate severity, height severity), three 20m×30m sample plots were set, and a total of 12 plots were set. Collecting soil samples from the field, soil total nitrogen, soil bulk density and other physicochemical properties as well as soil organic carbon (SOC), soil labile organic carbon (readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC)) were measured. Variance analysis was used to analyze the differences and trends in change of soil organic carbon components under different fire severities. Correlation analysis and redundancy analysis was used to explore the effect mechanism of forest fire on soil organic carbon from the point of view of soil physicochemical properties. The results showed that:(1) different fire severities significantly affected soil physicochemical properties, in which soil total nitrogen, available phosphorus, cation exchange capacity, capillary porosity, and total porosity increased with the increase of fire severity, while soil pH, available potassium, available nitrogen, and bulk density decreased with the increase of fire severity. (2) The SOC decreased with the increasing of fire severity, and the maximum decrease of 5-10 cm soil layer was 44.79%. With the increase of fire severity, the labile organic carbon of four kinds of soil decreased, which the decrease in 0-5 cm soil layer was the most obvious. Among them, the order of decrease of each component was ROC (36.31%-61.31%) > POC (30.05%-53.61%) > MBC (20.60%-8.19%) > WSOC (13.47%-29.29%). The different responses of different components to forest fire significantly affected the proportion of soil ROC, POC, and WSOC. (3) Soil organic carbon and its active components were significantly positively correlated with cation exchange capacity, capillary porosity, total porosity, available phosphorus, and available nitrogen (P<0.05), but significantly negatively correlated with bulk density (P<0.01). The variations of cation exchange capacity, bulk density, total nitrogen and water content after fire dominated soil organic carbon. Among them, cation exchange capacity had the greatest effect (61.7% explanation).