The rock-concrete composite interface is a weak part of engineering structures, and its shear mechanical properties are critical to overall structural stability. To reveal how chemical corrosion affects these properties, chemical corrosion and shear tests under different pH values (3,5,7) was performed, and the composite’s shear failure mode, shear strength characteristics, and mechanical parameter evolution was analyzed. The results show these as follows. Chemical corrosion induces mineral dissolution and composite mass loss; Lower pH and longer corrosion time increase the mass loss rate, with a maximum of 1.94%. It shifts the composite to a combined “shear-wear” failure mode. The shear stress-displacement curve has four stages (compaction, linear elasticity, peak failure, post-peak residual). Peak shear stress decreases with reducing pH (max deterioration rate: 33.64%), and the established shear strength prediction model is highly applicable. The shear parameters of the interface (shear stiffness, cohesion, friction angle) decrease with lower pH, with maximum deterioration rates of 33.09%, 30.39%, and 21.62% respectively; shear stiffness is most corrosion-sensitive. The results provides a reference for the design and stability analysis of composite related engineering structures.