Successful liver surgery requires a clear understanding of the differences in liver shapes and vessel distribution in different individuals. Furthermore, in clinical medicine, there is a high demand for surgical assistance systems for individual patients. Therefore, we aim to segment the liver on the basis of the CT volume data, semi-automatically extract the vessels from the segmented livers and then visualize the 3D shape and the extracted vessel distribution using a virtual operation system. In addition, to improve the operability and accuracy of information recognition in the virtual operation system, prior knowledge and the clinical experiences of doctors are integrated into the visualization system for a practical virtual surgery. A 3D visualization of the liver, allows the user to easily recognize abnormal regions, which need to be removed, and to simply select this region using a 3D pointing device. Furthermore, 3D visualization, allows details in the structure of the human liver to be better understood and a more practical surgical simulation system can be implemented in our developed system.