16MnR　is　the　typical　material　of　pressure　equipment　which　worked　under　complex　stress　state　in　engineering　application.　In　order　to　be　close　to　the　actual　combined　tension-shearing　stress　state　and　explore　the　relationship　of　deformation　capacity　and　different　stress　state,　many　groups　of　combined　tension-torsion　tests　on　16MnR　specimens　were　designed　and　the　equivalent　stress-strain　relation　under　different　stress　state　was　obtained.　The　concept　of　stress　triaxiaty　(TS　value)　was　cited　to　characterize　the　different　stress　state　and　the　result　showed　different　stress　states　have　a　great　influence　on　the　material　plastic　deformation　capacity,　TS　value　turns　larger,　the　plastic　deformation　weakened;　16MnR　has　a　strongest　plastic　deformation　capacity　in　pure　torsion;　the　level　of　tensile　stress　had　no　significant　effect　on　the　maximum　stress　in　the　biaxial　stress　state,　but　has　a　significant　inverse　relationship　with　the　maximum　equivalent　strain.At　last,　the　mathematical　relationship　between　maximum　equivalent-strain　and　stress　triaxiaty　could　be　found.　If　the　stress　state　of　one　point　in　the　engineering　structures　is　certain,　the　maximum　equivalent-strain　can　be　estimated.　©　(2013)　Trans　Tech　Publications,　Switzerland.