Due to the inadequate development of acetabulum and consequently the stress concentration in cartilage, acetabular dysplasia not only causes instability of the hip joint, but is also associated with the development of osteoarthritis. Periacetabular osteotomy is a useful treatment for acetabular dysplasia by moving the bone fragment, cut off from the bone around the acetabulum, to improve the actabulum coverage and contact stress distribution of the hip joint. However, there is still no effective and practical analysis technique that can demonstrate the effect of the operation and provide biomechanical data such as stress distribution for treatment. In this study, three dimensional models of pre-and post-operative acetabulum have been constructed, and then computer simulations for gate cycle have been performed to evaluate the biomechanical effect of the periacetabular osteotomy by applying finite element contact analysis.