Waterjet is a very useful technology for rock excavation because of low level noise and vibration during breaking rocks. To accurately predict the volume and shape excavated by the waterjet, it is important to understand waterjet fracture mechanisms. There have been various theoretical assumptions and approaches in the literature. In this study, waterjet mechanisms are classified into three standards: a mechanism scale, theoretical assumption for a target material, and jet phase. In addition, through a waterjet experimental study for weathered and intact granitic rocks, a fracture shape is observed and analyzed on comparison with the previous mechanisms. As a result, best waterjet mechanisms are selected to explain the fracture pattern of the granitic rocks.