BACKGROUND:Studies demonstrated that,the probability of middle and distal end of femur bone fatigue or fracture reaches maximum when the moving loads increase or under an impact load.OBJECTIVE:To analyze the stress-strain distribution,principle stress vectors and displacements of femur during gait.METHODS:The contour curves of femur and muscles attached to femur were extracted slice by slice based on the serial CT data from a healthy male volunteer,which were used to build musculoskeletal system models.And the straight-line muscle models of the lower extremities were constructed to evaluate muscles forces and joints forces by using a multi-objective optimization method based on gait analysis.The finite element models of femur during gait were built by taking muscle forces and joint forces as boundary conditions in ANSYS 10.0 to obtain the stress-strain distribution and displacements.RESULTS AND CONCLUSION:The maximal displacement occurred on the femur head,and the maximal stress occurred in the middle and distal end of femur during the whole gait.There exists bigger tensile stress in the location of the femur neck and middle and distal end of corpus ossis femoris.The result validates the fact that femur fracture often happens at the middle and below of femur stem from the viewpoint of biomechanics.