Abstract: Dynamic caustics experimental technique is used to study dynamic characteristics of the propagation of explosion main cracks and branched cracks under blasting stress wave. The prefabricated cracks were opening or closing as a result of the explosion stress wave reflection from these cracks, and reduced the dynamic behaviors of explosion main cracks. These main cracks can’t generally pass through the prefabricated cracks and continue to extend. The branched cracks are derived from the ends of the prefabricated cracks. The initiation and propagation of branched cracks are caused by the diffraction effective of tensile stress concentration of the prefabricated crack tips. The split angles of branched cracks are closely related to the prefabricated cracks and angle of blasting incidence stress wave. The branched cracks initiation is started from the direction of generalized maximum energy release rate, and shown as mixed mode fracture and the stability propagation with the direction of maximum principal stress. The dynamic stress intensity factor and velocity of branched cracks are lower than blasting main cracks’. The initial fracture toughness of branched cracks is about 0.5-0.65 MN/m3/2. The arrest toughness of branched cracks is about 0.25-0.35 MN/m3/2

Key words: explosion mechanics, blasting stress wave, prefabricated through crack, explosion main crack, branched crack propagation, dynamic caustics