Abstract: Compared with the traditional two-dimensional ultrasound,the three-dimensional ultrasound image can display the morphological features of tissues and organs more intuitively and stereoscopically. It is a hot spot in the field of ultrasound research. To improve the accuracy of 3D imaging,this study combines high-precision optical tracking system and freehand ultrasound image scan-ning to achieve three-dimensional reconstruction of freehand ultrasound images. 3D reconstruction requires the establishment of an ac-curate coordinate transformation system and accurate target extraction. In order to overcome the influence of large-angle rotation on ma-trix transformation during coordinate transformation,the system introduces the Rodrigue matrix method. In the procedure of target ex-traction,anisotropic diffusion filtering and level set segmentation are utilized to achieve accurate object extraction. Experiments show that the system is easy to operate and has a good effect in experimental teaching applications. It is of great help to promote students' ba-sic knowledge of ultrasonic image processing and 3D reconstruction technology.