In　this　paper,　a　self-expanding　bionic　flap　is　added　to　the　suction　surface　of　the　wind　turbine　S809　airfoil　to　suppress　the　separation　of　flow　around　the　airfoil　at　high　angles　of　attack.　This　is　inspired　by　the　phenomenon　in　which　birds　slightly　pop　up　their　feathers　at　the　wing　trailing　edge　under　special　conditions.　The　sample　spaces　of　the　bionic　flap　structural　parameters(including　the　flap　height　H,　the　distance　from　flap　to　the　trailing　edge　D,　and　the　popped　up　angle　of　flap　θ)are　obtained　with　the　Box-Behnken　response　surface　methodology(RSM).　The　lift-drag　ratio　of　the　airfoil　under　a　large　angle　of　attack　is　selected　as　the　optimization　target.　Numerical　calculation　and　quadratic　regression　analysis　are　also　carried　out　to　investigate　the　response　function　relationship　between　the　structural　parameters　of　the　bionic　flap　and　the　airfoil　lift-drag　ratio　as　well　as　the　optimal　combination　of　bionic　flap　parameters.　The　performance　of　the　bionic　flap　airfoil　and　clean　airfoil　are　compared　from　the　perspective　of　dynamic　and　static　aerodynamic　characteristics.　The　results　show　that　D　has　the　highest　sensitivity　to　lift-drag　ratio　among　all　the　single-factor　main　effects　while　θ　-H　has　the　highest　sensitivity　to　lift-drag　ratio　among　all　the　interaction　effects;　the　bionic　flap　suppresses　the　flow　separation　on　the　suction　surface,　and　changes　the　size　and　distribution　of　the　separation　vortex　and　the　wake　vortex　at　high　angles　of　attack,　thus　suppressing　the　dynamic　stall　effect.　As　a　result,　the　lift-drag　ratio　and　lift　are　increased　at　most　by　53%　and　41.8%　respectively　under　different　configurations.　©　2022　Xi＇an　Jiaotong　University.　All　rights　reserved.