Due　to　the　potential　influence　of　constraint　effect　on　failure　assessment,　a　link　is　needed　to　bridge　the　constraint　effect　characterized　by　higher　order　term　asymptotic　solution　and　time　dependent　failure　assessment　diagram　(TDFAD).　In　this　paper,　a　modification　method　for　creep　toughness　incorporating　C(t)-A(2)(t)　theory　is　proposed　based　on　Nikbin-Smith-Webster　model.　The　relation　between　Q-term　and　A(2)(t)-term　is　also　presented　for　creep　crack.　Results　show　that　the　creep　toughness　can　be　influenced　by　constraint　parameter　remarkably.　A　modified　TDFAD　is　proposed　based　on　C(t)-A(2)(t)　solution.　Based　on　the　creep　data　of　316H　stainless　steel　and　various　compact　tension　specimens,　the　modified　TDFAD　curves　considering　constraint　effect　characterized　with　A(2)(t)-term　is　presented　and　discussed,　which　indicates　the　important　role　of　constraint　effect　on　the　assessment　boundary　of　TDFAD.　The　research　given　in　this　paper　can　provide　an　alternative　method　in　which　the　constraint　effect　can　be　included　in　TDFAD　under　high　temperature.