The　main　shaft　serves　as　a　critical　component　in　the　wind　turbine　transmission　system,　and　carries　the　torque　transmitted　by　the　turbine　hub.　However,　the　surface　of　the　main　shaft　is　vulnerable　to　fatigue　cracks　under　the　external　harsh　environmental　factors.　And　the　cracks　are　a　serious　threat　to　the　safe　operation　of　the　turbine.　To　detect　these　defects,　an　electromagnetic　acoustic　transducer　designed　to　fit　the　central　hole　of　the　spindle　was　introduced.　Based　on　the　Lorentz　force　effect　and　the　magnetostriction,　the　finite　element　simulation　model　of　the　EMAT　transducer　was　established,　to　analyze　the　acoustic　beam　deflection　angle　and　acoustic　field　intensity　change　range.　Also,　the　details　analyze　the　law　of　influencing　factors　on　transducer　efficiency,　such　as　magnet　size,　number,　layer　number,　coil　splitting　and　so　on.　The　optimized　transducer　detects　effectively　surface　defects　on　the　spindle　sample　in　the　crack　detection　experiments.　Moreover,　the　sector　scanning　detection　of　surface　cracks　can　be　demonstrate　by　adjusting　the　frequency,　and　the　defect　positioning　error　is　less　than　3　mm.　©　The　Author(s),　under　exclusive　license　to　Springer　Nature　Switzerland　AG　2023.