Fatigue　crack　initiation　and　propagation　behaviours　were　studied　based　on　the　dynamic　response　simulation　by　the　three-dimensional　finite-element　analysis　(FEA)　and　dynamic　response　experiments　for　tensile-shear　spot-welded　joints.　The　entire　fatigue　propagation　behaviour　from　the　surface　elliptical　cracks　at　the　initiation　stage　to　the　through　thickness　cracks　at　the　final　stage　was　taken　into　consideration　during　the　three-dimensional　FEA　dynamic　response　simulations.　The　results　of　the　simulations　and　experiments　found　that　the　fatigue　cracks　of　spot-welded　joint　from　initial　detectable　crack　sizes　to　crack　propagation　behaviour　could　be　described　by　three　stages.　Approximately　one-half　of　the　total　fatigue　life　was　taken　in　stage　I,　which　includes　micro-crack　nucleation　and　the　small　crack　growth　process;　20%　of　the　total　fatigue　life　in　stage　II,　in　which　the　existing　surface　crack　propagates　through　the　thickness　of　sheet　and　30%　of　the　total　fatigue　life　in　stage　III,　during　which　the　through　thickness　crack　propagates　along　the　direction　of　plate　width　to　the　final　failure.　According　to　the　relationship　between　the　crack　length　and　depth　and　the　dynamic　response　frequency　during　the　simulated　fatigue　damage　process,　the　definition　of　fatigue　crack　initiation　and　propagation　stages　was　proposed.　The　analysis　will　provide　some　information　for　the　fatigue　life　prediction　of　the　spot-welded　structures.