Abstract: Objective: To analyze the femoral stress distribution changes after total hip replacement mechanically, and to provide a theoretical foundation for the clinical practice Methods: Using the Sap84 finite element program, 3 kinds of models were analyzed Model A is normal femur, Model B is cementless prosthesis with supporting collar, and Model C is cemented prosthesis without collar Both Model B and Model C have 3 different stem lengths Results: 1.The stress distribution of normal femur is mainly in the internal aspect of the medial cortical femur, cementless prosthesis with collar is in the interface between the stem of the prosthesis and medial cortical femur, whereas in the cemented prosthesis without collar, the distribution of stress mainly locates in the interface between cement and prosthesis; 2.Stress on the cemented prosthesis with collar is less than that on the cemented prosthesis without collar 3.Stress decreases slightly on the tip of the prosthesis as the length of prosthesis increases Conclusion: Stress on the femur changes after artificial hip replacement, cement has buffer effect on the distribution of stress in the femur Increased prosthetic length can't reduce the stress significantly