The　aim　of　this　study　is　to　discuss　the　plastic　shakedown　and　true　stress　of　the　cyclically　loaded　pressure　vessel.　A　thin-walled　cylinder　pressure　vessel　is　made　according　to　actual　working　state　and　a　water　pressure　test　system　is　built.　The　vessel　is　loaded　to　different　strain　levels　of　plastic　deformation　first.　Then　it　is　loaded　cyclically　to　shakedown　state.　The　relationship　between　plastic　strain　and　shakedown　range　is　given　based　on　numerous　experiments.　The　constitutive　model　of　the　true　stress-true　strain　of　the　vessel　is　obtained.　The　experimental　results　show　that　the　ratcheting　obviously　occurred　when　the　vessel　is　cyclically　loaded　to　plastic　deformation.　The　true　stress-strain　constitutive　model　which　is　presented　in　this　paper　can　show　appropriately　the　constitutive　relation　of　the　vessel　when　it　is　under　multi-axial　stress　state.　The　application　of　uniaxial　shakedown　constitutive　model　has　been　demonstrated　in　this　study.　©　(2014)　Trans　Tech　Publications,　Switzerland.