The　characteristics　of　natural　frequency　were　investigated　based　on　the　simulation　by　3D　finite　element　analysis　and　the　dynamic　response　experiments　for　spot-welded　specimens　during　the　fatigue　damage　process.　The　fatigue　propagation　behavior　from　the　surface　elliptical　crack　at　the　initiation　stage　to　the　through　thickness　cracks　at　the　final　stage　was　taken　into　consideration　during　the　finite　element　dynamic　response　simulations.　For　two　kinds　of　fatigue　crack　propagation　behaviors,　the　changes　of　natural　frequency　were　simulated　by　the　finite　element　analysis.　The　results　of　the　simulations　showed　that　good　agreement　is　achieved　with　experimental　data.　The　number　of　mode　which　can　be　used　for　the　fatigue　damage　analysis,　is　identified　by　using　the　relationship　between　the　simulated　crack　length　and　the　natural　frequency.