The particle shape exerts a profound influence on the shear characteristics of granular material systems. In this study, the particle shape was characterized by aspect ratio, sphericity, and convexity. Moreover, the overall shape parameter was employed to quantitatively describe the particle shape. Direct shear tests were carried out on mixtures of spherical glass beads and angular glass sands at five different proportions (0%, 25%, 50%, 75%, and 100%), systematically investigating the effects of particle shape on the shear strength and dilatancy of granular materials. The experimental results indicate that at an initial relative density of 65%, all specimens exhibited strain softening and dilatancy behavior. As the overall shape parameter increases, both the internal friction angle and cohesion of the granular materials also decrease. Furthermore, with a decrease in the overall shape parameter, the dilatancy behavior becomes more pronounced, and the dilatancy angle also increases. To further elucidate the mechanism through which particle shape affects the shear strength of granular systems, the rate-state shear strength theory was introduced and validated. A parametric analysis was subsequently performed based on this framework. The theoretical analysis results indicate that the rate-state shear strength theory is reasonable and effective, and can well reflect the influence of particle shape on the shear strength of granular materials.