For most engineering materials, crack nucleation typically serves as a precursor to ultimate fracture, a process influenced by various microstructural features including grain orientation, grain boundaries, and precipitates. This work systematically investigated the fracture behavior of typical single-crystal and polycrystalline Ni-based complex concentrated alloys, revealing that microcracks tend to nucleate at high-energy locations such as grain boundaries and precipitate interfaces. In single-crystal alloys, due to the constraint effect of the γ matrix on cracks, cracks are compelled to propagate along the direction of maximum slip at their tips, exhibiting a zigzag crack propagation characteristic and resulting in relatively high fracture toughness. In contrast, in polycrystalline alloys, cracks readily nucleate at high-energy interfaces such as grain boundary carbides and propagate rapidly along grain boundaries, leading to premature fracture. The research results demonstrate that controlling crack nucleation and propagation behavior through rational adjustment of interfacial states and precipitate distribution characteristics can effectively enhance the fracture toughness and crack tolerance of materials.