Fatigue　crack　characteristics　are　investigated　based　on　the　dynamic　response　simulation　by　finite　element　and　the　dynamic　response　experiments　for　tensile-shear　spot-welded　specimens.　In　the　different　fatigue　damage　cumulative　quantity,　the　dynamic　response　frequency　is　measured　during　the　fatigue　damage　process.　The　results　show　that　the　natural　frequency　varies　non-linearly　with　the　fatigue　damage　fraction.　On　the　basis　of　the　relationship　between　the　crack　length　and　the　natural　frequency,　the　definition　of　fatigue　crack　initiation　stage　is　proposed.　Fatigue　crack　initiation　life　is　predicted　by　the　local　stress　and　strain　approach　with　the　proposed　fatigue　crack　initiation　stage　for　tensile-shear　spot-welded　specimens.　The　results　show　that　good　agreement　is　achieved　with　experimental　data.