The effect of design features of an internal spinal fixator under loading is critical to understanding of interaction between fixator and instrumented spine. In this study, we performed finite element analysis for spinal pedicle screw installed in the lumbar spine. The purpose of this study is to model and simulate the newly designed spinal pedicle screw. The deformation and stress of the screw are analyzed for the tightening process and loading process simulating the condition when it is installed in the human body as described in the ASTM F1717 procedure. We expected this study is to derive reliable results for developing a new model by analysis of design variables and fatigue behavior.