The　monopile　is　one　of　the　most　common　solutions　for　the　foundation　of　offshore　wind　power　plants.　The　p-y　curve　recommended　by　API　is　commonly　used　to　obtain　the　horizontal　displacement　of　a　monopile.　For　piles　of　a　more　than　2　m　diameter,　the　p-y　curve　model　overestimates　the　initial　stiffness　of　subgrade　reaction　and　yields　inaccurate　horizontal　displacement.　An　evaluation　of　the　current　p-y　method　was　made　to　obtain　the　key　factors　responsible　for　overestimating　the　initial　stiffness　of　subgrade　reaction.　These　key　factors　were　amended.　A　modified　p-y　curve　model　was　proposed　in　which　the　nonlinear　impact　of　the　dimeter　and　depth　on　the　initial　stiffness　K　was　considered　based　on　the　calculation　results　of　FLAC3D.　The　developed　p-y　curve　model　was　compared　with　test　data　and　the　results　of　the　current　p-y　curve　and　the　previous　modified　model.　The　results　show　that　the　good　agreement　between　the　calculated　results　of　the　developed　modified　p-y　model　and　test　values　verified　the　rationality　of　the　modified　p-y　model.　Copyright　©2021　Engineering　Mechanics.　All　rights　reserved.