In order to explore the blast-induced crack propagation behavior in rock mass with two vertical prefabricated defects, a series of blasting experiments of models with double vertical cracks were carried out based on digital laser caustics. The evolution process of blast-induced crack is shown and the effect of single-hole charge on the crack propagation behavior (crack propagation length, stress intensity factor, propagation velocity, and initiation time, et al) in rock mass with defects was explored. The results show that the crack propagation length, propagation velocity, crack initiation toughness and stress intensity factor at the end of the double vertical cracks increase with the increase of single-hole charge. For crack J_u, the effect of single-hole charge on crack propagation velocity is small, and the limit velocity of crack propagation is about 0.38 times of the shear wave velocity. For cracks D_l and D_r, the initiation time decreases, but the peak stress intensity factor increases with the increase of single hole charge. Besides, the stress intensity factor and propagation length of crack D_r increases significantly compared with crack D_l. The crack D_l starts to crack earlier than the crack D_r when the energy of the blasting stress wave acting on both ends of defect B is enough to cause the crack to propagate on both sides. The increase of charge in a single hole can increase the propagation velocity of crack D_r, but has little effect on the propagation velocity of crack D_l.