<p>To explore the mechanical properties and evolution mechanism of rocks with different fissure inclination angles and penetration depths, discrete element simulations have been done on samples with different fissures using PFC2D with “FISH” language. The mechanical characteristics, acoustic emission traits, crack propagation patterns and rupture angle of samples under triaxial compression have been examined. Based on the modified strain energy density criterion theory, the crack initiation mechanism has been analyzed, revealing the relationship among fissure inclination angle, rupture angle and Poisson's ratio of double-fissured rocks. Experimental and simulation results show that confining pressure restricts the failure of pre-existing fracture planes and enhances the mechanical properties of rocks. Under triaxial compression, peak stress is linearly related to fissure inclination angles, penetration depth and confining pressure. Peak strain increases with confining pressure, while the elastic modulus exhibits a nonlinear development trend with both fissure inclination angle and penetration depth. Failure mechanisms include tensile failure and shear-tensile composite failure. Crack initiation position has been affected by confining pressure and propagation rate has been inhibited. From the modified strain energy density theory, at same Poisson's ratio, rupture angle increases with fissure inclination angle, obvious change. At same fissure inclination, it increases slowly with Poisson's ratio, weak change. Under different angles and Poisson's ratios, confining pressure significantly affects rupture angle with consistent change. When pressure is small, rupture angle decreases slowly, weak sensitivity. When large, it increases rapidly, strong sensitivity. This study can offer a reference for underground rock engineering's safe construction and disaster prevention.</p>