Abstract: Presplit blasting technology is currently widely used in blasting engineering. In order to investigate the effect of pre-crack formed by split blasting on the dynamic fracture behavior of blasting cracks and original cracks,a series of studies were carried out based on the digital laser dynamic caustic experiment. The real-time dynamic parameters of crack propagation were obtained. The results show that the pre-crack can stop blasting-cracks from expanding to the re- tained rock mass and increase the damage of the explosive rock mass. The wing cracks generated at the both ends of the pre-crack expand to the retained rock mass. As the pre-crack length increases,the wing crack propagation length increases. The shorter pre-crack ( L = 20 -80 mm) can promote the propagation of the original crack in the retained rock mass. Only when the pre-crack length increases to a certain degree (L = 100 mm),it can inhibit the expansion of the original crack in the retained rock mass. When the length of the pre-crack A is 100 mm,the crack propagation length of B is 21% comparing with no pre-crack A model,and the average speed of Bz and By is 0 and 64. 8% without pre-crack A. When the pre-crack exists,the crack time of the ends of the primary crack increases with the increase of pre-crack length. When the pre-crack length increases to a certain extent ( L = 100 mm),explosive flank crack does not crack,By crack initiation time is delayed to the same 150 μs as without pre-crack. Fracture toughness of explosive flank crack is less than fracture toughness of backside flanking crack. When the pre-crack exists,the fracture toughness of the ends of the primary crack is less than that of the non-pre-crack,and the fracture toughness of explosive flank crack decreases with the increase of the pre-crack length. The peak of the ends of the primary crack stress intensity de- creases with the increase of pre-crack length.