Abstract: Geotechnical granular materials are often subjected to three-dimensional anisotropic stress under real stress state, where the initial stress anisotropy has a certain influence on the macroscopic and microscopic mechanical properties during subsequent loading and unloading processes. Specimens with different initial anisotropic stress states were prepared using the discrete element method (DEM), and a series of true triaxial tests were conducted under constant mean principal stress with loading in different directions. Strength envelopes were plotted for specimens with different initial anisotropic stresses on plane, and the variation of microscopic structural during the loading process to the same point on the strength envelope and the topological structure of strong contact networks before and after the peak strength were analyzed. It is found that before the peak strength, the initial anisotropic stress has little influence on the strength envelope of granular materials. The shape of the strength envelope after the peak strength is similar to the shape of the strength envelope before the peak strength, but the strength envelope after the peak strength has the smaller yield stress. During the loading process to a specific point on the strength envelope, the initial differences in the internal microscopic structures of the specimens diminish rapidly in the early stages of loading and gradually converge as loading progresses. Specimens with the same initial anisotropic stress before and after the peak strength exhibit significant differences in the internal contacts and the topological structure of strong contact networks, despite being under the same stress state, which may be an important factor that affecting the three-dimensional strength of granular materials.