This paper represents a novel 4-dimeiisional(4D) computer-based motion simulation system for patients having had Total Hip Arttiroplasty(THA). By constructing the skeletal model of the patient's lower extremity and measuring daily motions, we simulated the movement of the inner structures including the skeleton and the artificial joint. This system visually represents not only the 3-dimensional(3D) anatomical structure but also the 4-dimensional dynamic functions that represent the time sequential transitions of the position of each component. Clinicians can get detailed information of the movement of the hip joint quantitatively and give precise guidance for the patients with regard to postoperative daily motions. The measurement error was evaluated by performing experiments using OpenMRI and the results indicated sufficient accuracy of this system. We believe that this system enables clinicians to reveal the causes of complications after THA and encourages the development of new surgical techniques, materials, and designs of prostheses.