A　damage　mechanical　model　has　been　proposed　from　the　theory　of　continuum　damage　mechanics　that　describes　the　service　damage　evolution　of　steam　turbine　blade　materials　during　long　term　service.　In　the　model,　the　damage　variable　is　selected　according　to　the　variation　in　fatigue　limit　of　the　blade　materials　after　service.　Furthermore,　a　model　of　the　degradation　of　fatigue　strength　during　service　has　been　created.　The　experimental　results　are　in　good　agreement　with　the　model.　Compared　with　the　low　cycle　fatigue　damage　model,　the　strength　design　of　the　blade　is　conservative　early　in　its　service　life.　If　the　degradation　in　fatigue　strength　is　not　taken　into　account,　the　life　prediction　of　the　blade　is　inadequate　for　long　term　service　lives.　(C)　2001　IoM　Communications　Ltd.