Abstract: The defective cracks were prefabricated on the wall of the notch holes by using PMMA material，which were parallel or vertical to the notch, and the distance from the defective cracks to the centre of the holes was 2mm, 3mm and 4mm. The influence of notch hole wall defects on the expansion of notch blast cracks was investigated by using a digital dynamic caustic experimental system with numerical simulation. At the same time, TATP explosives were employed as a charge, which served to mitigate the effect of gun smoke on the dynamic caustic experimental system and to improve the experimental design. The results demonstrate that the reflection of the stress wave at parallel defects results in a downward shift in the direction of crack initiation at the notch, but the refraction of the stress wave at vertical defects don't affect the direction of crack initiation. The presence of wall defects in the hole impedes the impact of stress waves and blast gases on the cracks at the notch, resulting in a reduction in the length, expansion rate, and strength factor values of the cracks, and the degree of inhibition is contingent upon the distance of the defects from the centre of the borehole. As the distance between the parallel defects and the centre of the borehole increases, the inhibition effect of the parallel defects on both sides of the notch cracks gradually decreases; the inhibition effect of vertical defects on the far side of the notch cracks gradually decreases, while the inhibition effect on the proximal side of the notch cracks gradually enhances. The left and right notch cracks of vertical defects are more significantly affected by the boundary reflected stress wave than those of parallel defects. The left side notch cracks don't show an obvious pattern due to the pre-existing reflected stress wave at the defects; however, the right side notch cracks are significantly reduced by the boundary reflected stress wave with the vertical defects moving away from the centre of the notch holes.