To　comprehensively　illustrate　the　fatigue　damage　evolution　mechanism,　a　pair　of　high-speed　gears　in　a　1.5　MW　wind　turbine　was　selected　as　the　research　object.　Based　on　the　geometric　similarity　between　Voronoi　diagram　and　polycrystalline　structure,　a　mesoscopic　tooth　surface　model　was　established　with　Voronoi　tessellation.　Cohesive　elements　were　inserted　in　the　model　to　simulate　the　fragmented　effect　of　grain　boundary　on　matrix.　The　bilinear-separation　curve　being　related　to　cohesive　elements　was　used　to　evaluate　whether　the　damage　originates　or　not.　Then,　jumping-in-cycles　(JIC)　loading　method　was　applied　to　simulate　the　cyclic　cumulative　effect　of　contact　loading　due　to　gear　meshing.　As　a　result,　the　initiation　location　and　initiation　life　of　contact　fatigue　crack　were　simulated　and　predicted,　and　the　effects　of　wind　speed　change　and　friction　coefficient　on　crack　evolution　were　discussed.　Results　show　that　the　damage　evolution　rate　is　relatively　slow　at　the　initial　stage,　and　gradually　increases　with　the　loading　process　and　damage　accumulation.　For　the　investigated　gear　and　its　working　conditions,　the　first　two　cracks　appear　at　the　depth　of　0.13　mm　and　0.27　mm　under　the　gear　surface.　Initial　cracks　grow　gradually　under　cyclic　loading　of　contact　stress,　and　finally　form　typical　surface　spalling　failure.　Additionally,　higher　wind　speed　and　worse　lubrication　condition　will　significantly　reduce　the　life　of　wind　turbine　gears.　©　2022,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.