Femoral neck fracture is one of serious healthcare problems in aging societies. Osteosynthesis with implants is widely used for femoral neck fracture treatment, however, complications such as bone refracture around implant insertion holes may occur during postoperative rehabilitation period. Authors had already numerically analyzed osteosynthesis with implant under a static loading condition. In order to resolve the mechanics of the complications, we should analyze under the dynamic loading condition corresponding to gait motion. The purpose of this study is to evaluate not only time dependent stress distribution but also maximum stress concentration around proximal femur by using finite element analysis under the dynamic loading condition. First, three-dimensional hip joint finite element model was reconstructed from CT image. This model consists of the pelvis, proximal femur and implants (Hansson pin and Dual SC Screw). Then, dynamic loading and boundary conditions were applied to the model for simulating a gait motion. The dynamic loading around the hip joint was obtained from inverse dynamic analysis of a human gait using in-house musculoskeletal model Time varying stress distribution during a gait cycle was analyzed by using dynamic explicit method (AB AQUS ver.6.13-5). We examined the time varying von Mises stress distribution at the representative points located on the cortical surface. These simulation results successfully demonstrated the excessive stress concentration around the insertion holes induced by the gait motion. It is proofed that the proposed dynamic analysis has the capability of the refracture risk assessment of the osteosynthesis of femoral neck fractures.