Abstract: In order to study the fracture characteristics of semi-disc specimens with circular defects under different impact speeds, Hopkinson rod is used to dynamically load the semi-disc specimen, and the fracture process of the semi-disc specimen is observed by the dynamic caustics test system, Through the combination of the two test systems, the fracture characteristics of the semi-disc specimens are studied, the research results show that: before the crack initiation, the focal speckle radius jumps, which is caused by the repeated loading of the incident rod. With the increase of the impact velocity, the peak stress intensity factor of the crack passing through the circular defect increases, and the propagation speed of the crack passing through the circular defect also increases significantly, which shows that the impact velocity contributes to the crack propagation. With the increase of the radius of the circular defect, the stress intensity factor of the second crack initiation at the circular defect becomes larger.