Digital medicine is an important development of the modern medicine and the computer-aided surgery is an important part of the digital medicine. Applications of digital techniques in the computer aided preoperative planning are elucidated in the paper. Techniques of computer-aided design and computer aided manufacture have been widely used in the fields of customized prosthesis replacement, design and manufacture of customized surgical tools and medical auxiliary instruments and here some clinical cases are introduced. The fundamental technologies used in the surgical navigation and related clinical applications are also explained. The development trend of the computer aided surgery is described and it is concluded that the computer-aided surgery has a bright future.