Based　on　the　mechanical　characteristics　of　TC4　titanium　alloy　welded　joints　applied　in　ships　and　naval　vessels　etc,　this　paper　modified　the　existing　non-linear　continuum　damage　model　according　to　the　fourth　strength　theory,　and　proposed　a　new　non-linear　continuum　damage　model　that　was　better　in　conformity　with　engineering　practice.　The　model　parameters　were　estimated　according　to　the　fatigue　experimental　data.　Then　the　correctness　of　the　modified　damage　model　was　carried　out　according　to　the　observation　and　analysis　of　the　fatigue-unloaded　specimens　by　SEM.　By　comparing　the　modified　non-linear　damage　model,　the　linear　damage　model　and　experimental　data,　the　results　show　that　the　linear　damage　model　was　relatively　conservative　in　estimating　the　fatigue　life　with　medium　or　low　load,　but　the　modified　non-linear　damage　model　had　higher　accuracy　and　agreed　well　with　the　experimental　data.