Large　monopile　is　widely　used　in　offshore　wind　farm　due　to　their　relatively　simple　installation.　Monopiles　are　customarily　designed　by　applying　the　p-y　method.　That　being　said,　there　is　no　detailed　and　uniform　interpretation　on　the　reasons　for　limitations　in　the　current　p-y　method.　An　elaborate　study　is　performed　to　determine　the　main　reasons　of　such　limitations.　In　this　study,　a　FLAC3D　model　is　presented　to　evaluate　the　current　p-y　method　for　piles　in　sand　of　three　different　relative　densities　under　a　static　load,　in　which　the　non-linear　modulus　is　taken　into　account.　The　results　show　that　the　initial　stiffness　of　the　p-y　method　is　overestimated　and　even　more　magnified　in　the　large　depth.　The　diameter　effect　should　be　taken　into　account　under　diameters　exceeding　3m　in　loose　and　medium　sand,　as　well　as　diameters　more　than　5m　in　dense　sand.　©　Published　under　licence　by　IOP　Publishing　Ltd.