The　fatigue　damage　and　evolution　of　microstructure　in　a　CuW80　tungsten-copper　alloy　after　cyclic　loading　were　investigated　by　SEM.　The　parameters　of　fatigue　damage　were　quantitatively　analyzed　based　on　three-point　bending　fatigue　testing.　The　results　show　that　the　process　of　fatigue　damage　can　be　divided　into　three　stages　according　to　the　curves　of　fatigue　damage　parameters　vs　loading　cycles.　It　is　characteristics　of　dual　linear　damages　that　are　corresponding　to　two　stages　of　fatigue　cracks　initiation　and　propagation,　and　the　fatigue　lives　of　fatigue　cracks　initiation　and　propagation　take　about　60%　and　33%　of　whole　fatigue　lives,　respectively.　It　is　noticed　that　fatigue　cracks　initiation,　propagation　and　fracture　appear　only　inside　of　the　copper　grain,　not　on　the　boundary　between　tungsten　and　cooper,　or　not　inside　of　the　tungsten　grain.