This　study　involved　full-life　monitoring　of　high-cycle　fatigue　damage　evolution　in　stainless　steel　cruciform　joints　with　undercuts　and　their　control　groups,　using　acoustic　emission　technique.　Based　on　continuum　damage　mechanics,　the　wavelet　packet　subband　energy　of　acoustic　emission　signals　was　used　as　the　damage　variable　to　investigate　the　relationship　between　fatigue　damage　and　acoustic　emission　signals,　to　quantitatively　assess　the　extent　of　fatigue　damage.　The　research　findings　indicated　that　the　wavelet　packet　subband　energy　effectively　captured　the　fatigue　damage　evolution　process　in　both　defective　and　non-defective　specimens.　The　fatigue　damage　evolution　strips　obtained　from　processing　acoustic　emission　signal　data　using　nonlinear　normalization　method　demonstrated　insensitivity　to　fatigue　stress　amplitudes.　The　wavelet　packet　subband　energy　exhibited　excellent　identification　ability　for　early-stage　fatigue　damage　and　its　development　before　macroscopic　crack　formation.　This　study＇s　outcomes　were　expected　to　provide　strategies　for　identification　and　quantitative　assessment　of　fatigue　damage　in　welded　structures　throughout　their　entire　service　life,　as　well　as　predicting　remaining　life.　©　2024　Elsevier　Ltd