Objective To investigate biomechanical properties of the femur during slow walking and stair climbing before and after total hip replacement (THA), so as to provide theoretical basis for optimal design and manufacturing of the prosthetic hip. Methods The 3D finite element model of hip femur was established and validated first, and the stress distributions and stress shielding rates during slow walking and stair climbing before and after THA were calculated. Results During slow walking, the stress increased gradually from the proximal femur to the distal femur, reaching the maximum 90.6 MPa at the lower part of the femur before THA. A stress shielding phenomenon occurred on the femur after THA, but the stress amplitude decreased, with the maximum stress reaching 82.5 MPa. The maximum shielding rate appeared near the greater trochanter of the proximal femoral prosthesis and the total stress shielding rate reached 14.9%-99.0%. In addition, excessive stress concentration occurred at the prosthetic neck. Meanwhile, the stress distribution during stair climbing had a similar regular pattern as that appeared during slow waling, but with a more obvious stress shielding effect. Conclusions The greater stress shielding of the proximal femur and the excessive stress concentration on the prosthetic hip during stair climbing will both influence the THA surgery quality, so patients should minimize the movement involving large joint angle after THA.