<p>The failure behavior of rocks subjected to complex loading conditions is significantly affected by microcracks. The traditional strength criteria often fail to fully account for the role of microcracks in the brittle failure of rocks, and cannot reveal the microscopic failure mechanism of rocks, leading to discrepancies in predicting the strength behavior of rocks under true triaxial compression. Based on the mixed-mode fracture criterion and further incorporating the influence of the friction coefficient on the penny-shaped crack surface, this paper proposes a micromechanics-based three-dimensional nonlinear strength criterion, which aims to address the nonlinear effects of the intermediate principal stress on strength characteristics of rocks subjected to true triaxial compression. By comparing with experimental data, the favorable agreement between the theoretical strength and the experimental results is validated to precisely predict the strength characteristics of rocks subjected to true triaxial compression.</p>