In the process of large diameter pile hole construction for landslide treatment， rapid drilling is the key to success. Therefore， the selection of appropriate drilling tools and technology is extremely important， and the pneumatic DTH hammer is widely used because of high drilling efficiency. With the pneumatic DTH hammer drilling process， the spherical teeth on the bottom of the bit break rocks to achieve high drilling efficiency； however， inappropriate selection of impact energy for the spherical teeth can lead to increased energy loss， quick tooth wear and low drilling efficiency. Appropriate selection of impact energy is of great significance to rock fragmentation. In this paper， ABAQUS software is used to simulate the rock impact process by a single spherical tooth， and the free-fall impact experiment is carried out on the impact hammer to analyze the rock fragmentation mechanism of a 19mm diameter spherical tooth by at different impact energy， together with the change pattern of the broken area. The results show that the rock crushing mechanism can be divided into three stages： elastic deformation， fracturing and volume crushing. When the spherical teeth drills granite at 30 J impact energy， energy loss can be effectively reduced and rock crushing efficiency can be improved.