Applying the method of finite element analysis, the finite element model of sub-frame of an automobile was built. With the aid of MSC software, longitudinal force operating mode which was pre-verified to be the most critical mode, was chosen for the static strength analysis and fatigue life simulation analysis of the sub-frame. Then the stress and fatigue life nephograms of the sub-frame were gotten. Comparison between finite element analysis and experiment result indicated that the finite element model can practically and properly reflect the real stress distribution of the sub-frame. Finally, based on this finite element model, some structure optimizations were done. After structure optimizations, the stress level was obviously improved. This method of FEA simulation together with experimental verification, significantly reduces the development cycle of new products, and is of important value in product design and quality improvement.