RI turbine is a device that rotates the shaft by the working fluid enters the radial direction and exit in the axial direction. It is mainly used in automobile turbochargers and helicopters. Turbocharger is an important part of reducing fuel use as part of the vehicle’s power source. It is largely divided into compressor part and turbine part, and rotates the compressor by the power received from the turbine part. The gas emitted after combustion in the engine is the working fluid and the driving force for rotating the turbine. In this process the turbine is directly exposed to hot combustion gases. There is an intermediate cooling process, but the trend is to reduce and simplify it. Therefore, thermal stress analysis and optimal design process for the blades of the turbocharger turbine is required. In this study, the optimal design of turbine blade was carried out to alleviate thermally vulnerable areas without compromising efficiency through CFD (computational fluid dynamics) and RSM (response surface method). After preliminary design, numerical analysis was used to identify thermal weakness, and the optimal design was carried out with vulnerable area and efficiency as output parameters. As a result, a blade design that can lower the temperature from the weakness was derived, and a thermal optimization design process of the RI turbine was presented.