The　high-cycle　fatigue　behavior　was　investigated　in　pure　titanium　after　surface　nanocrystallization　(SNC　Ti).　Compared　with　the　coarse-grained　titanium　(CG　Ti)　samples,　the　SNC　Ti　samples　exhibit　an　improved　fatigue　life.　The　SNC　has　a　remarkable　influence　on　the　fatigue　cracks　initiation　and　growth　of　pure　titanium.　The　results　show　that,　because　the　free-surface　cracking　is　suppressed　by　the　surface　nanogradient　structure　in　the　SNC　Ti,　the　fatigue　cracks　initiation　sites　change　from　the　free　surface　to　the　subsurface.　Meanwhile,　the　fatigue　crack　growth　rate　decreases　due　to　the　microstructural　feature　and　residual　compressive　stress.　The　deformation　twins　in　the　subsurface　of　SNC　Ti　have　a　marked　effect　on　the　fatigue　crack　initiation　and　the　crack　growth.　The　former　effect　is　due　to　the　twin　boundaries　being　preferential　sites　for　crack　initiation,　while　the　latter　is　associated　with　the　barriers　that　the　twin　boundaries　pose　to　the　propagation　of　dislocations.　Furthermore,　microstructural　analysis　indicates　that　the　dislocation　distribution　in　SNC　Ti　gradually　becomes　homogenous　as　fatigue　processes.　This　homogeneous　microstructure　is　also　beneficial　to　the　improvement　of　fatigue　life.