Abstract: The stability of soil aggregate organic carbon is an important indicator for evaluating the soil's carbon sequestration capacity, nutrient retention capacity, and its response to external environmental changes. To clarify the impact characteristics of tunnel engineering construction on soil aggregates and their organic carbon, three fixed monitoring plots (TC1, TC2, TC3) in the impact area of the railway project were set up along three altitude gradients (3240 m, 3420 m, and 3600 m). The non-impact area was used as the control (CK1, CK2, CK3). Based on analysis of variance (ANOVA), the impacts of tunnel construction on soil aggregates and the stability of their organic carbon were explored from the perspectives of soil physical and chemical properties, aggregates, and aggregate organic carbon. The results showed that the physical properties such as moisture content and porosity in TC area, and the mass and stability of soil aggregates, were significantly affected by tunnel construction (P<0.05). In both TC and CK areas, the chemical properties such as pH value, nitrogen, and phosphorus, as well as the contents of total aggregate organic carbon, easily oxidizable organic carbon, soluble organic carbon, and inert organic carbon, were not affected by tunnel construction (P>0.05), but showed significant differences under the influence of altitude and soil layer (P<0.05). Three-factor ANOVA combined with correlation analysis indicated that tunnel construction directly damaged the soil structure, reduced the stability of soil aggregates, and significantly affected the physical protection mechanism of soil aggregates that maintained the stability of aggregate organic carbon. There were no significant changes in the litter biomass, enzyme activity, microbial biomass carbon, and aggregate organic carbon components in the study area, indicating that tunnel construction had no significant impact on the plant and microbiological regulatory mechanisms that maintained the stability of aggregate organic carbon. Therefore, tunnel construction did not affect the stability of soil aggregate organic carbon.