In this study, smoothed particle hydrodynamics (SPH) is utilized to simulate the dynamic behavior of rock under blast. In the simulation, the Johnson-Holmquist (JH2) damage model is employed to model the rock damage and fracture under blasting loads. The effects of air and water as coupling material and copper inside of the borehole are considered. A penalty based node to node contact model is introduced on the interfaces of the different SPH parts to avoid interface effects. The simulated 3D blast-induced fractures are validated by comparing with available experiments. It is found that the crack propagation is asymmetrical around the borehole, despite the apparent isotropy and homogeneity of the simulated rock. The numerical results indicate that the SPH approach used in this work can be applied to effectively simulate densely cracked region, radial cracks and circumferential cracks of rock subjected to blast loading.