Abstract：According to the view of random arrival time of incident wave，theoretical analysis is carried out on the dynamic fracture regulation of rock bar. Through theoretical calculation of pure tensile stress caused by the superposition of incident compressed waves and reflect tension waves after triangle stress wave，rectangle stress wave and exponential attenuating stress wave propagate to the free end of one-dimensional homogeneous rock bar in several specific incidence periods. The possibility of fracture，the potential fracture time，numbers and length of rock bar are systemically analyzed. The relationship among the numbers and length of fracture and the peak value of stress wave and incident time is established；meanwhile，the inherent essence of random phenomenon in rock dynamic fragmentation is disclosed.
