Though　material　tensile　test,　fracture　and　fatigue　tests,　hardness　test　and　microstructure　analysis　for　deactivated　crystal　reactor　vessel,　the　maximum　stress　and　deformation　were　obtained　in　danger　zone　at　the　bottom　crystal　vessel　by　finite　element　method　and　the　rupture　strength　and　fatigue　life　of　crystal　vessel　were　also　analyzed　and　calculated.　Combining　the　analyses　about　stress　corrosion,　corrosion　fatigue　and　creep　deformation,　it　is　pointed　out　that　the　failure　of　crystal　vessel　is　a　brittle　fracture　under　the　co-activation　between　corrosion　fatigue　and　creep.