There is a limit in expense and facilities to perform structural analysis by repeating crash tests using actual vehicles. This paper describes an example of crash analysis by FEM performed by our company, for frontal crash and rollover of a large-sized bus. Regarding the frontal crash analysis, firstly static collapse tests were performed using a scale model of the under-floor structure in order to get the deformation mode, then the structure was analyzed using an FE model. Secondly, an effectiveness of a full model that included the frame model was verified by a frontal crash test at 35km/h. Last, the structural improvement based on the full model was considered. Regarding the rollover analysis, since the event duration is long, a method to utilize partial body model instead of a complete vehicle was proposed in order to reduce calculation time. As practical results, the improved vehicle showed good performance satisfying the target level in frontal crash and rollover tests.