In this paper a new method to develop femur longitudinal section outlines from cross section CT images is introduced. The femur longitudinal section outlines developped from cross section CT images and its corresponding calculation process differ from the femur Xray images chiefly in two advantageous aspects. First, in one view direction, many femur longitudinal section outlines at different depth can be achieved instead of only one outline obtained from X ray film. In addition, the femur longitudinal section outlines developped from crossaee whole femur. That is unable to sive a precise relationship among the different rectional outlines. The precise femur outline developped with this method can be used to ensure a more precise design of arificial hip joint.