The shear resistance of sandstone-mudstone particle mixture is an influence factor for the foundation treatment of port engineering in mountainous areas. We carry out the direct shearing tests of consolidation drainage to 48 groups of samples with different mudstone particle contents，normal stresses and water bearing states by the direct shear apparatus，analyze the effect of different mudstone particle contents on the form of shear stress displacement-curves，reveal the relationship between deformation and strength，and establish the empirical calculation method of shear strength. The results show that the particle contact can be divided into homogeneous particle contact and heterogeneous particle contact. Under the effect of stress concentration，mudstone particle breakage is an important factor affecting strength and deformation of sandstone-mudstone particle mixture. The stress-strain curve of sandstone-mudstone particle mixture is mainly strain hardening，and its shear strength decreases with the increase of mudstone particle content.