Abstract： Objective To compare biomeehanical characteristics of dynamic hip screw(DHS) versus proximal femoral nail anti-rotation (PFNA) in fixations under different apparent bone densities and loads in a three-dimensional finite element model of osteoporotic intertrochanteric fracture of the femur (modified Evans-Jensen type Ⅲ ). Methods CT was used to scan the upper and middle femur of an aged male with osteoporotic intertrochanteric fracture (modified Evans-Jensen type Ⅲ ).He was 75 years old, 172 cm in height and 70 kg in weight.Based on the CT scans,fracture models were created to simulate reductions and DHS internal fixation (Model Ⅰ group) and PFNA internal fixation (Model Ⅱ group).Each group was subjected to 7 apparent bone densities (70％,80％,90％,100％,110％,120％ and 130％ ) and 3 loads (0.5,1.0 and 3.0 times of weight).The 2 model groups were compared under all working conditions in terms of the maximum Von Mises stress of the femur,the maximum Von Mises stress of internal fixator and femoral element failure ratio. Results Under the same load,the stresses and femoral element failure ratio sustained by Model Ⅰ group were all significantly greater than by the Model Ⅱ group ( P ＜ 0.05).In the same model group,the stresses and femoral element failure ratio sustained by the femur and the internal fixator increased significantly with the increase of load ( P ＜0.05).Under the working condition of 3.0 times of weight load and 70％ of apparent bone density, Model Ⅰ group and Model Ⅱ group respectively had the femoral maximum Von Mises stresses of 84.702 MPa and 38.986 MPa,the maximum Von Mises stresses of internal fixator of 952.557 MPa and 580.134 MPa, and the femoral element failure ratios of 3.25％ and 7.99 × 10-3％. Conclusion For osteoporotic intertrochanteric fracture of the femur (modified Evans-Jensen type Ⅲ ), PFNA internal fixation system has an obvious biomechanical advantage over DHS,because the former may provide greater fixation stability than the latter,and unlikely leads to internal fixation failure.