Abstract: The outer vacuum cryostat is a large-scale (D = 38 m, H = 39.6 m) vacuum container located on the outer side of the China Fusion Engineering Test Reactor (CFETR) device. It is designed to provide a stable high vacuum environment for the internal superconducting magnets of the CFETR device. The cryostat is subjected to operational conditions that include 100 cycles of vacuum pumping and 500 cycles of vacuum chamber baking. However, under these operational conditions, the weak regions of the cryostat are susceptible to fatigue cracking due to thermal cyclic loading caused by 1 atmosphere pressure and 200℃ baking. Such fatigue cracks can lead to the development of cracks, leakage, and eventual failure of the entire vessel. Therefore, this study focuses on the fatigue simulation analysis of the cryostat structure at the locations of maximum stress and critical positions during vacuum pumping and vacuum chamber baking cycles using the finite element method. The analysis results provide insights into the overall stress distribution of the cryostat under thermal cyclic loading of 1 atmosphere pressure and 200°C baking and allow for an evaluation of its fatigue life after failure. These findings serve as a theoretical basis for verifying whether the cryostat meets the usage requirements and provides a foundation for optimization. The analytical approach employed in this study can also be applied to similar devices for analysis and evaluation purposes.