The thesis primarily focuses on the comprehensive evaluation of the novel roof step cut technique for hip dzsplasia cases by combining clinical and engineering mechanics analysis. Patients with hip dysplasia from our department were included and received the roof step cut (RSC) technique. During postoperative follow-up, with X-ray and bone scintigraphy the absorption of the grafted bone, loosening of the components and bone graft viability were evaluated at different time points. For functional assessment, the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Oswestry Disability Index (ODI) were used both preoperatively and postoperatively. For the mechanical study, the CT scan of a patient with DDH was used to reconstruct a 3D pelvis model. Arthroplasty 3D components were assembled using the software of Ansys SpaceClaim. 4 finite element analysis (FEA) models based on the RSC technique and bulk bone graft (BBG) technique as well as the direction of the screw insertion direction were established and were respectively named Harris0, Harris45, RSC0, and RSC45. The primary analysis focused on the following two aspects: (1) stress distribution and total deformation of bone graft and screws; (2) the pressure and sliding distances at three contact surfaces: bone graft-acetabulum, bone graft-metal cup, metal cup-acetabulum. In the results, no signs of graft resorption were observed throughout the follow-up period. Bone scintigraphy showed that the mean region of interest (ROI) counts activity ratio (graft vs. reference) for the whole body were gradually decreased along with time and for SPECT of the graft, the corresponding values showed a gradually increasing trend. The WOMAC and ODI scores showed significant improvement after surgery. The mechanical study showed that the maximum stress and total deformation in the Harris models were considerably higher than in the RSC models. The stress distribution values of the screws in the RSC models were significantly lower than those in the Harris models. The maximum total deformation followed a similar trend. When the screws were inserted at 0°, the highest value was located close to the center of the screw, while when inserted at 45°, the highest value moved to the outer 1/3 area. The maximum pressure and sliding distance showed a decreasing trend from models of Harris0 to RSC45. When the BBG was fixed with screws at 45 degrees (the Harris45 model), the contact between the metal cup and the acetabulum showed notable instability with larger sliding distance. The pressure at the bone graft-metal cup contact was presented with a significant high value. Therefore, Roof step cut technique is a feasible method to reconstruct the acetabular roof for hip dysplasia cases. The short/mid-term clinical outcome meets the purpose of the intervention. The RSC technique effectively reduces stress and deformation on both the graft and compression screws. Additionally, it decreased the pressure and sliding distance at the contact surfaces between the components.