The hip joint diseases have various kinds of origination, and they have multifarious forms according to the originations. One of the major concerns to plan the surgical operation for the hip diseases is the alternation of biomechanical environment, such as joint force and contact pressure. In this study, we analyzed the biomechanical effects of surgical techniques of the hip joint diseases by finite element analysis. We developed the finite element models of the pre-operative and post-operative hip joints for four children patients who have hip joint disease with abnormal joint anatomy. The models consist of two bones (pelvis and femur) reconstructed from CT images, and the articular cartilages on acetabulum and femoral head. Bones and cartilages were assumed having linear elastic material properties. The resultant joint force and the abductor force were calculated from 3-D static equilibrium in one-leg standing position. The calculated joint force was applied on the pelvis, the inferior plate of femur was fixed in all directions, and the medial edge of pelvis was constrained in vertical direction. Mechanical values such as contact force, pressure, and contact area on the hip joint were measured. The results of the finite element analysis were similar with those clinically estimated. The present non-destructive biomechanical evaluation method could be clinically useful for the optimal planning and selecting of surgical method by the rearrangement of contact pressure in the hip joint.