Abstract: To reveal the formation mechanism of the loess-mudstone dual slope landslide from the micro and macro structures, triaxial shear tests, determination of soluble salt composition, and mineral content were carried out for the overlying loess, underlying mudstone, and sliding zone soil. The macro-phenomena were studied from the failure mode of the soil and the law of shear strength changing with water content. The grey correlation method was used to determine the correlation between the shear strength of the slip zone soil and soluble salt and mineral components to explore the internal relationship between the microstructure and macro strength of the slip zone soil. The main failure mode of the slip zone soil is dilatancy, which is closely related to its internal crystal structure. With the increase of water content, the shear strength parameters of the soil showed that the decreasing of the internal friction angle was greater than the cohesion. The correlation between peak strength and cohesion and K⁺+Na⁺and SO₄^2- content is greater than 0.8,displaying a greater correlation. The correlation between the internal friction angle and HCO₃^- and K⁺+Na⁺content is greater than 0.7,reflecting a greater correlation. In terms of the whole rock mineral combination of the sliding zone soil, the peak strength and cohesion of the sliding zone soil are mainly affected by the content of alkali feldspar, clay minerals, and plagioclase, while the internal friction is mainly affected by the content of clay and quartz. The analysis of clay minerals indicates that the peak strength, cohesion, and internal friction angle of the slip zone soil are mainly affected by the content of illite and chlorite. Illite has a significant effect on the internal friction angle of the slip zone soil. The research results of this paper can provide a reference for the landslide warning research of loess-mudstone dual structure slope.