[Objective] The key mechanisms by which amorphous iron oxide regulates the mechanical properties of Benggang soil were analyzed from a microscopic perspective in order to provide a theoretical basis for the prevention and control of Benggang erosion. [Methods] Kaolinite, the dominant clay mineral in soil from a typical Benggang area of Fujian Province, was selected as the research object. By incorporating amorphous iron oxide at different concentrations(1, 2, 3, and 10 g/kg) into kaolinite and utilizing X-ray diffraction(XRD), scanning electron microscopy(SEM), and direct shear tests, this study analyzed its regulatory effects on soil microstructure and shear strength parameters. [Results] XRD analysis revealed that amorphous iron oxide did not undergo a chemical reaction with kaolinite but primarily altered mineral characteristics through physical coating. The concentration of amorphous iron oxide significantly influenced the distribution of cemented aggregates across different particle sizes, demonstrating a pronounced regulatory role in the formation of aggregates within the 2—250 μm range. Among microstructural parameters, only particle long-axis and roundness exhibited significant changes. The long-axis decreased by 22% in samples with the 3 g/kg treatment, while roundness was reduced by 25% in samples with the 2 g/kg treatment. The coefficients of variation for all other parameters remained below 15%. The treatment with 3 g/kg consistently exhibited the highest shear strength across all confining pressure levels. The enhancement in shear strength was closely associated with the observed microstructural alterations. Further analysis indicated that the 3 g/kg treatment resulted in the most substantial improvement in cohesion, which increased by 24.82% compared to pure kaolinite. In contrast, the internal friction angle varied by less than 5.30%. [Conclusion] Amorphous iron oxide enhances soil shear strength by optimizing soil structure through cementation and encapsulation.