Abstract: With the progress and development of nuclear power technology, the GEN-Ⅳ nuclear power plant has gradually begun to be commercialized, and its main steam parameters can reach the level of conventional thermal power ultra-high pressure steam turbines, but the characteristics of the high-pressure outer cylinder are very different from those of thermal power units and PWR nuclear power units.In this paper, the strength, rigidity and steam tightness of the outer cylinder of the GEN-Ⅳ ultra-high pressure nuclear power turbine are analyzed and evaluated comprehensively by the finite element method, and a variety of optimization measures are taken to make the cylinder performance meet the design requirements.