Abstract: The shape of particle greatly influences the shear behavior of granular materials. The quantitative evaluation indexes of 3D morphology of irregular particles is lacking incurrent studies. In this paper, the PFC3d is used to simulate the 3D direct shear condition, and the model verification and parameter selection are completed by comparing the experimental results. The length and direction of each axis of the particles equivalent ellipsoid are determined by the particle tensor rotation matrix. Based on the equivalent ellipsoid, the calculation formula of the 3D angularity index is improved. The influence of particle shape on the mechanical properties of granular materials is analyzed. The results show that the shear stress increases nonlinearly with the shear strain and has obvious extreme values. The morphology of the stress-strain curves of different shaped particle groups is different. The shear strength and internal friction angle increase linearly with the natural logarithm of the AI (Angularity Index). The relationships can be fitted with a logarithmic function, indicating that the slope of the line of the internal friction angle and the natural logarithm of the AI is 7.621, and the intercept is 63.653.