Abstract: Through direct shear tests on argillaceous mica schist with different schistosity inclinations and water contents, the influence mechanism of schistosity inclination and water content on the shear mechanical properties of mica schist was revealed. Combined with PFC^2D simulations, the distribution law of mesoscopic cracks in the rock mass was clarified, and the failure pattern of the rock mass was proposed. Based on the proposed failure pattern, a shear fracture mechanical model of mica schist was established, and a theoretical formula for its shear strength applicable to any schistosity inclination was derived. The results show that the cohesion of the rock mass increases linearly with increasing schistosity inclination, while the internal friction angle first increases and then decreases. A decrease in water content increases both cohesion and internal friction angle, with cohesion being more sensitive to water content than the internal friction angle. Three main failure patterns of mica schist are identified: shear failure along the schistosity; partial shear failure along the schistosity combined with partial tension-shear failure across the schistosity; and tension-shear failure at the ends with shear failure in the middle. As schistosity inclination increases, the number of shear cracks on schistosity surfaces first increases and then decreases, while the total number of cracks, shear cracks, tensile cracks in the rock matrix, and tensile cracks on schistosity surfaces all increase. The theoretical values of shear strength agree well with the experimental results.