Abstract：It is an effective new method to make further analysis of crack propagation for blasting fracture with dynamic caustics. Using a plexiglass sample and by means of shadow optical method of caustics，the different features of dynamic variation in stress (or strain) field，plastic area，and nucleation zone (shadow area) during loading and unloading are studied. The propagation，termination，and mode of blasting cracks are presented. An accurate termination tenacity value is achieved；and preliminary cracks are extended rapidly under blasting stress wave. A full of strain energy accumulates in the top of blasting crack；and the mode of caustics of latter crack is close to the common dynamic caustics. The majority of blasting cracks is a process of unloading fracture.
