To study the influence of thermo property on stress of femur-prosthesis system quantitatively, the finite element method is used to analyze the stress of femur-prosthesis system when the hip joint has been replaced, in which the prosthesis, bone cement and femur are assumed as linear elastic and isotropic materials in shape of a concentric cylinder. Considering the thermal effect, the axial stress of prosthesis, bone cement, femur and the interface shear stress along axial of the prosthesis／bone cement and bone cement／femur when the prosthesis are made of titanium alloy and cobalt-chromium alloy are acquired separately by mechanical analysis and FEM simulation.The results indicate that the interface failure is the primary failure mode of the femur-prosthesis system. The existence of thermal effect accelerates the interface failure of femur-prosthesis system and the loose of prosthesis stem. The possibility of interface failure which result in operation failure will ascend when the cobalt-chromium alloy is used, because the thermal expansion coefficient of cobalt-chromium alloys is higher than that of titanium alloy.