Vegetation composition is a crucial factor driving changes in soil functions within forest ecosystems. To clarify the impacts of species diversity and soil cementing substances in different forest types on soil aggregate stability in the Zhangguangcailing Mountains, this study took three typical forest types in the Zhangguangcailing Mountains, namely dark coniferous forests, spruce-fir mixed coniferous-broadleaved forests, and montane poplar-birch forests, as the research objects. We comparatively analyzed the differences in soil aggregate stability and the changes in the contents of cementing substances among different forest types, quantified the contributions of organic and inorganic cementing substances to soil aggregate stability, and used the partial least squares path model to analyze the internal mechanism by which species diversity affects soil aggregate stability through organic and inorganic cementing substances.The research results showed that: (1) The particle size range of soil aggregates in the three forest types mainly concentrated in the range of 2-0.25 mm. Among them, the soil aggregate stability of spruce-fir mixed coniferous-broadleaved forests was significantly higher than that of the other two forest types (P<0.05). (2) Compared with dark coniferous forests, the total aggregate organic carbon in spruce-fir mixed coniferous-broadleaved forests and montane poplar-birch forests increased by 57.1% and 44.2% respectively, the total particulate aggregate organic carbon increased by 56.9% and 48.4% respectively, and the total mineral-bound aggregate organic carbon increased by 66.3% and 71.3% respectively. The contents of the above three types of aggregate organic carbon in dark coniferous forests were significantly lower than those in the other two forest types (P<0.05). (3) In terms of complexed iron oxides, the order was montane poplar-birch forests > spruce-fir mixed coniferous-broadleaved forests > dark coniferous forests, while there were no significant differences in amorphous iron oxides and free iron oxides among different soil layers (P>0.05). (4) The partial least squares path model indicated that species diversity had a direct and extremely significant negative effect on the content of iron oxides (path coefficient: -0.459, P≤0.001), had a direct positive effect on aggregate organic carbon, but it did not reach a significant level (P>0.05). Soil iron oxides had a significant positive effect on soil aggregate organic carbon (path coefficient: 0.349, P≤0.05), and had a positive effect on soil aggregate stability, but it was not significant. Soil aggregate organic carbon had an extremely significant positive effect on soil aggregate stability (path coefficient: 0.693, P≤0.001).In conclusion, the soil aggregate stability of spruce-fir mixed forests is the highest. Organic cementing substances play a direct regulatory role in soil aggregate stability, while inorganic cementing substances mainly have an impact through indirect pathways. The influence of different forest types on soil aggregate stability is mainly mediated by soil cementing substances: changes in forest types directly act on inorganic cementing substances, which in turn affect the accumulation and transformation processes of organic cementing substances, and ultimately change soil aggregate stability. The upper vegetation indirectly regulates soil aggregate stability by mediating the form of iron oxides and influencing the interaction between iron oxides and soil aggregate organic carbon. The results of this study provide a theoretical basis for clarifying the coupling mechanism between soil aggregate stability and cementing substances in forested dark brown soil.