Fixation nail systems , such as DHS, DCS and the standard Gamma-nail, are widely applied for the 31-A2 intertrochanteric unstable fractures treatment, but which one would be of more curative effect is still remained as a disputed problem. In this work, precise femur model with 31-A2 fracture was rebuilt based on the CT data, and fixation nail models were built by CAD. By the means of finite element analysis (FEA), the biomechanical data of femur and nail systems were achieved under typical loading. The results show that under the same load, the maximal stresses on the fracture sections for DCS, DHS and Gamma nail systems are 48MPa, 24MPa and 19MPa, separately; and the directional deformation is the highest with DCS fixation systems, while lowest with Gamma nail fixation system. Considering the mechanical safety, Gamma nail is more suitable for 31-A2 intertrochanteric unstable fractures treatment.