Abstract: Granite residual soil in hot and humid areas often causes problems such as shallow slope failure and soil erosion due to its strong disintegration characteristics, and its disintegration process is significantly affected by changes in environmental acidity and alkalinity. This study investigates the influence of pH on the disintegration behavior and micro-mechanisms of granite residual soil through disintegration tests conducted over a wide pH range(3-13), combined with Zeta potential measurements, laser particle size analysis, and scanning electron microscopy observations. The results show that the disintegration patterns can be classified into a linear type(pH=3-11)and an inverse"L"-shaped two-stage type(pH=12-13). The slope of the disintegration curve can serve as a quantitative index for evaluating disintegration resistance. Variations in pH affect the surface charge and dissolution-coagulation behavior of kaolinite and iron/aluminum oxides, thereby altering interparticle interactions. In neutral to acidic environments, dissolved cations inhibit particle detachment. In weakly alkaline conditions(pH=8), electrostatic attraction dominates, resulting in the strongest disintegration resistance. In strongly alkaline environments(pH=12-13), competition between gel confinement and strong electrostatic repulsion leads to a slow-rapid two-stage disintegration. Disintegration under strongly alkaline conditions is dominated by the detachment of individual kaolinite platelets(micrometer scale), whereas under neutral-acidic conditions it primarily involves the separation of"pseudo-sand" sized aggregates. This study provides a theoretical basis for understanding the disintegration mechanisms of granite residual soil under varying pH conditions and for developing targeted chemical stabilization techniques.