Abstract: The influence of offset crack on dynamic impact fracture behavior is studied using the digital-leaser dynamic caustics system in conjunction with impact loading device.An inner mother crack along loading direction and its offset edge crack in PMMA were employed.The initiation and propagation behavior,as well as the caustics patterns of both cracks are observed.Some important dynamic fracture parameters of mother crack,such as the initiation time,maximum speed and dynamic stress intensity factor,are analyzed with different offset distance.The results show that the radio of crack spacing to crack offset distance is virtually important to the initiation time and maximum speed of mother crack,which are also influenced by the location of both cracks in the midline of the specimen.Moreover,the changes of dynamic intensity factor of mother cracks with different crack spacing are found to be similar,while the time of their maximum values are quite different.