Abstract: The crack propagation and coalescence mode play an important role in the step-path failure mechanism of rock slopes. By using the discrete element method (DEM), the coalescence modes between two pre-existing cracks with different geometries (rock bridge angle) and confining stresses under biaxial compression are performed. Three types of cracks can be identified during the tests, which are the secondary coplanar cracks, secondary inclined cracks and wing cracks. Meanwhile, the wing cracks and secondary inclined cracks occur under a low confining stress biaxial compression and almost disappear under a high confining stress. Based on the above, the step-path failure mechanism of multiple flaws is investigated. It is found that the crack coalescence modes depend on the coalescence stress severely, and the extended modes are carried out and show the homologous view. Finally, taking a rock slope as an example, the mechanism of rock slope step-path failure is generalized. The coalescence of the joints is from bottom to upper, and the coalescence mode of the joints is subjected to the slope stress conditions. Based on the modes of crack coalescence and correlation between crack coalescence modes and stress, three zones of the failure surface are divided.