Objective To investigate and analyze the orthopaedic morphology of re-dislocation after reduction of hop joint dislocation by using 3-dimensional computer tomography.The causes of re-dislocation were analyzed.Methods Twenty-eight cases of developmental dislocation of hip joint with re-dislocation were analyzed by quantitative and qualitative parameter using 3-D CT,and compared with some normal ones.Results The results show that the angle between femoral neck and femoral diaphysis in re-dislocation group were larger than no re-dislocation group and normal one.The incidence of severe deficient of superior acetabulum in re-dislocation group was higher than group with successful operation.The anterior angle of femoral neck was significant difference between re-dislocation and normal group.There was no difference between group of re-dislocation and group with successful operation.Conclusions The causes of re-dislocation of hip joint reduction may be correlated with the angle between femoral neck and femoral diaphysis and the defect of superior acetabulum rim.