A good positioning technique is essential for obtaining accurate diagnostic information in radiography. In this study, we developed the X-ray positioning simulator of the radiography which could assist the students to train the positioning practice by using CT images. First, from the CT image data of the phantom scanned beforehand, we constructed the three-dimensional (3D) phantom by using solid model and we performed the positioning on a personal computer (PC) using the 3D phantom. Next, we calculated the plane image corresponding to the displayed phantom position from the CT image data. By using our proposed method, it was expected that students could perform the positioning training at the same time without having to expose X-rays and develop the films.