The investigation on failure patterns and paths of cracked rock slopes under excavation unloading is one of the hot issues in the slope engineering field. Accurate identification of the potential failure path is of great significance for excavation safety and support design of the slope. A theoretical method for crack propagation discrimination was embedded into the numerical simulation based on the fracture propagation analysis method, and the quick simulation of initiation, propagation, and coalescence of discontinuous cracks in rock masses was realized through stress intensity factor calculation at crack tip, crack propagation pattern recognition, crack initiation angle derivation, and crack propagation and coalescence. The proposed simulation method was used to analyze the crack propagation mechanism and the failure path of a highway cutting slope under multi-stage excavation unloading. The results show that during the multi-stage excavation from top to bottom of the slope, the crack initiation first occurs at the bench edge, and then a dominant propagating crack is formed through tensional propagation. With the downward excavation of the slope, the dominant crack gradually propagates downward the slope in tensile-shear mixed pattern and coalesces with existing cracks, forming a step-path failure in the middle and upper parts of the slope. When the crack propagates to the lower part of the slope, the crack propagation pattern transforms from tensile-shear mixed pattern to shear pattern, and finally the potential sliding body slides out along an arched shear surface at the slope toe. This study reveals a composite failure pattern of the cracked rock slope under multi-stage excavation unloading, which includes the tensile-shear mixed propagation pattern with a step-shaped path in the upper part and the shear propagation pattern with an arched path in the lower part, and can provide new ideas for the support design and construction stability control of rock slopes.