Abstract: The dispersive soil is a kind of special water sensitive soil, which is often modified with lime and other soil solidification materials. However, for slope engineering, due to the complex construction process of modification treatment, the cost is high and the effects often fail to meet the design requirements. The influencing factors and action mechanism of in-situ thermal reinforcement of dispersive soil are studied through the dispersion discrimination tests such as mud ball, fragment, pinhole and double-hydrometer, as well as the micro tests such as microstructure detection, X-ray diffraction and infrared spectrum analysis. The test results show that the temperature, heating time and degree of compactness have significant effects on the thermal reinforcement of the dispersive soil. With the rise of the temperature, the extension of the heating time and the increase of the compactness, the dispersibility of the dispersive soil decreases gradually until it is eliminated. When the heating temperature is lower than 200℃, the dispersity of the dispersive soil is weakened, but it is reversible. When the temperature is higher than 200℃, the dispersibility of the dispersive soil is completely lost and irreversible. After high temperature treatment, through the condensation of dehydrated particles and the deformation and cementation of salt minerals, the particle agglomeration structure is enhanced, the dissolution of water-soluble ions is reduced, the soil alkalinity is reduced, and the thickness of electric double-layer is reduced. Then, the gravity between soil particles is greater than the repulsion, and the dispersion is weakened or even disappears. This study indicates that the in-situ thermal reinforcement technology is a promising technology for the stability of problematic soil slopes.