Abstract: In order to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. X-ray diffraction test is used to analyze the changes of the mineral composition of the granite before and after filling with water. The Hopkinson device is used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact damage were selected for electron microscope scanning test to analyze the fracture failure characteristics. Fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact damage and the scanning image of the fracture under electron microscope, and the influence of the image magnification selected during electron microscope scanning on the fractal dimension was discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportion of hornblende, albite, microcline and quartz in the saturated granite decreases, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases, while the fragmentation degree and the fractal dimension of block gradually increase, and the influence of initial damage on the fractal dimension of block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning image increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering reference for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.