Abstract: At particle scale, the morphological characteristics have a significant effect on the mechanical responses of sand. To analyze such effect, a modified 3D shape factor $S^{\prime }$ is introduced to quantify the particle shape. The particles with the designed shape are fabricated through the 3D printing technology. The mechanical responses of the particles are obtained in the direct shear tests performed under a range of normal stress levels and relative packing densities. The data analysis shows that the difficulty of estimating the effects of particle shape on strength using 2D shape factors can be effectively overcome by the shape factor $S^{\prime }$. The maximum and minimum void ratios have internal correlations with the values of $S^{\prime }$. The comparison of the 3D printed soil analog and natural soil particles demonstrates the serviceability of 3D printed particles as substitutes for sandy materials in the laboratory. In addition, the critical state friction angle is found to increase with the increase of value of $S^{\prime }$, but both the peak dilation angle and the peak internal friction angle are found to increase initially then decrease after reaching the peak, for the reason that irregularity promotes looser packing. This observation indicates that there exists an optimal particle shape factor of granular materials in nature. Finally, the relationship between $S^{\prime }$ and mechanical properties is established to provide theoretical basis for considering the effects of particle shape in engineering design and numerical simulations.