［Objective］ The response of soil aggregate grain size composition and stability and the organic carbon content of all aggregate levels to simulated warming were analyzed to provide a scientific basis for the dynamic changes in soil structure stability and carbon storage capacity of the Pinus tabulaeformis plantation forest in Daqingshan Mountains， Inner Mongolia， in the context of climate warming. ［Methods］ Soil samples were collected from a depth of 0—40 cm from a P. tabulaeformis plantation on Daqing Mountains， Inner Mongolia. Based on a four-year field warming experiment， wet sieving was used to separate the soil into three aggregate size fractions， namely， >0.25 mm， 0.25—0.053 mm， and <0.053 mm. The organic carbon content of each aggregate fraction was measured. ［Results］ Microaggregates were the dominant fraction in the study area. Warming reduced the content of macroaggregates and microaggregates in all soil layers. Meanwhile， the content of silt-clay aggregates increased significantly by 14.92%， 14.01%， and 13.84% in each layer， respectively. Compared to the control， the mean weight diameter （MWD） and geometric mean diameter （GMD） of soil aggregates decreased significantly under warming. The MWD decreased by 5.93%， 3.66%， and 5.68% in each layer， whereas the GMD decreased by 8.83%， 8.41%， and 10.63%， respectively. Under both treatments， the organic carbon content was the highest in the silt-clay fraction. Warming increased the organic carbon content in the silt-clay fraction but decreased it in the macroaggregate and microaggregate fractions. The total organic carbon content increased in the surface soil layer but decreased in the 10—20 cm and 20—40 cm layers. Under warming conditions， the silt-clay fraction contributed the most to the SOC. Compared with the control， the contribution rate of organic carbon in the silt-clay fraction increased by 44.39%， 39.60%， and 43.31% in each layer， respectively， followed by the microaggregate fraction. The macroaggregate fraction had the lowest contribution. ［Conclusion］ Warming altered the composition of soil aggregates， destabilized the soil aggregate structure， and reduced the organic carbon content in macro-and microaggregates， indicating that warming was detrimental to the physical protection of soil organic carbon.