•A novel simulation method for massive concrete structures with cracks is proposed.•Refined simulation model with irregular cracks is established based on the method.•The method reduces meshing difficulty in complex 3D models with cross-scale cracks.•Crack propagation during dam construction and under an earthquake is examined. The irregular cross-scale cracks in massive concrete structures threat the safety. Due to huge difference in scale between structures and cracks, the stability of the irregular cross-scale cracks (millimeter level) cannot be accurately analyzed in the massive concrete structures (hundred-meter level). The imprecision of the mesh model is incompatible with existing advanced cracking methods. To address the problem, this paper presents a novel numerical simulation method for irregular cross-scale cracks in massive concrete structures with node projection strategy. The elements that the crack passes through are identified on the original mesh model without cracks, and the numerical simulation model with irregular cracks is generated by projecting the corresponding nodes of elements that the crack passes through onto the crack point cloud. The primary advantage of this method is that it does not require modifying the original element types or meshing the geometric model with cracks. To verify the present method, the three-point bending beams of concrete with regular cracks and irregular cracks are examined with experiment and numerical simulation. It demonstrates that the shape characteristics of an irregular crack can result in distinct tension damage patterns compared to a regular crack. In addition, the crack propagation during dam construction and earthquake loading is investigated to demonstrate the applicability of the present method for simulating crack propagation in massive concrete structures.