We have applied a simulation using 3D-CAD-based digital mockup to the behavior evaluation of variable geometry turbochargers (hereinafter referred to as VG turbochargers) developed for passenger-car gasoline engines that can comply with exhaust gas regulations (RDE : Real Driving Emission) , which regulate emissions under actual vehicle running situations in which the engine is required to generate a significant amount of torque and function at wider speed range . This method uses a combination of flow/heat transfer analysis that sets boundary conditions and structure/mechanism analysis that is used for reliability evaluation. We have established this evaluation method for matters related to the reliability of VG turbochargers used for gasoline engines, which are subject to higher temperatures than diesel engines, such as the damage and deformation due to thermal stress and the wear of mechanical parts and implemented it to product development.