The effects of confining pressure and particle breakage on the mechanical behavior of tailings were investigated using the discrete-element method to simulate conventional triaxial tests. The particle breakage was simulated using the octahedral shear stress breakage criterion and 14 Apollonian fragments replacement method. The macroscopic behavior of tailings revealed that the peak shear stress ratio is sensitive to confining pressure and the critical shear stress ratio is less sensitive to particle breakage. Confining pressure and particle breakage affect shear expansion, leading to changes in shear damage patterns. The quantitative study shows that particle breakage is the main factor influencing the nonlinear variation of the tailing strength. However, the influence proportion of particle breakage is gradually decreasing with the increase in the confining pressure. Microscopic analysis reveals a positive correlation between the overall anisotropy and the shear stress ratio, with the anisotropy of the normal contact force distribution contributing the most. The variation of the overall anisotropy is caused by the variation of the contact state, in which the sliding contact state is the main influencing factor.