Drill and blast method has been widely used as an effective excavation method for underground rock caverns or tunnels. To achieve a good blast design, an understanding on the rock dynamic response and rock fragmentation process is important. In this paper, numerical simulations are performed on a typical parallel hole cut blasting based on the discontinuous deformation analysis (DDA). The blast loading is obtained from the explicit FEM code LS-DYNA and the dynamic response of the rock mass is modeled by the DDA. Different influence factors on rock fragmentation under the blast loading are investigated, including the different delay time and various rock mass properties. Such a study will have potential applications for better drill and blast designs.