On　the　basis　of　the　dynamic　response　measurement　during　the　fatigue　process,　fatigue　damage　and　life　prediction　are　studied　for　single　spot-welded　joint　made　of　galvanized　low　carbon　steel　materials　(Steel　grade　as　BJXH50)　for　automotive　body　under　variable　amplitude　loading.　Fatigue　test　is　carried　out　under　variable　amplitude　loading,　and　the　data　of　dynamic　response　frequency　is　extracted　by　measuring　dynamic　response　during　the　fatigue　damage　process.　The　characteristics　of　natural　frequency　change　are　analyzed　during　the　fatigue　process　under　constant　and　variable　amplitude　loadings.　The　natural　frequency　ratio　(NFR)　is　defined,　and　the　damage　is　denoted　by　the　NFR.　It　is　proposed　that　the　effect　of　load　level　is　reflected　by　the　NFR　and　current　cycles.　By　the　NFR　and　current　cycles,　fatigue　life　prediction　model　is　proposed,　which　can　avoid　errors　generated　from　load　spectra　analysis　and　damage　calculation.　The　results　show　that　good　agreements　are　achieved　with　the　calculated　fatigue　life.　©　2009　Journal　of　Mechanical　Engineering.