In-situ　observation　was　carried　out　on　fatigue　crack　growth　in　centrifugal　spray　deposition　(CSD)　Ti-48Al-2Mn-2Nb　alloy　with　self-made　SEM　fatigue　loading　stage.　The　results　show　that　the　fatigue　crack　propagates　with　increase　of　cyclic　stress　level,　while　the　cyclic　number　has　a　little　effect　on　it.　The　lamellar　structure　has　a　great　influence　on　fatigue　crack　propagation　by　torturing　the　crack　growth　path　and　changing　the　crack　propagation　direction.　TEM　observation　shows　that　deformation　twinning　is　sensitive　to　the　cyclic　stress　level,　and　at　the　high　cyclic　stress　level　a　large　amount　of　deformation　twins　can　be　found,　indicating　that　cyclic　twinning　becomes　the　dominant　deformation　mode　at　this　stress　level.