Osteoporotic patient has low bone quality and often occur unstable fracture. Conventional dynamic hip screw method can provide good result on stable femoral fracture. On the unstable femoral fracture, it has high failure rate. The purpose is to investigate the biomechanics analysis for dynamic hip Screw on osteoporotic and unstable proximal femoral fracture. The specific aims are to :(1) develop the osteoporotic and unstable proximal femoral fractures model,(2) investigate the influence of lesser trochanter fixation on stress and deformation distribution. This study total reviewed 130 patients treated by dynamic hip screw surgery and classified the fracture according to AO system. Statistic data showed that the common unstable femoral proximal fracture type is A2.1 (AO classification). The osteoporotic femur model of finite element method (FEM) was developed from the CT image of 80 years patient. Loading condition assigned single-leg stance. The FEM analytic result show the lesser trochanter has a moment of rotation in dynamic fixation without wires fixation condition. Using wires to fix the lesser trochanter can enhance the structure stiffness and reduce the stress distribution in unstable intertrochanter fracture (A2.1 type).