Craniotomy has been widely used in the treatment of many craniocerebral diseases due to its good controllability and low recurrence rate. Aiming at the problems of saw blade jamming and poor cutting quality during craniotomy, this paper proposes a new ultrasonic cranial cutting device. It connects ultrasonic transducers, amplitude rods and saw blades in series and applies axial high-frequency mechanical vibration to the saw blades. The high-speed rotary motor drives the saw blade to rotate and cut through belt transmission, by changing the vibration frequency of the transducer, the modal of the saw blade is changed to achieve different cutting effects. Firstly, based on the half-wavelength design method, the structure of the amplitude rod was designed and a three-dimensional finite element model was established. Through ANSYS modal analysis and structural optimization, the natural frequencies that meet the working requirements were obtained is 25 kilohertz and 41 kilohertz. Then the structure of the circular saw blade is optimized according to these two natural frequencies, so that the saw blade can also obtain two modes that meet the working conditions at the corresponding frequencies. Finally, based on ABAQUS simulation software, the skull cutting under different ultrasonic frequencies and speeds is simulated, and the stress generated during cutting is compared. The results show that increasing the cutting speed increases the cutting stress to some extent. When cutting the skull, the external excitation frequency of 41 kHz is more stable than 25 kHz, and the average cutting stress is lower. Compared with ordinary cutting methods, ultrasonic assisted cutting method is beneficial to reduce cutting stress and improve cutting quality.