When　the　top　of　a　pile　in　soft　ground　is　subjected　to　a　large　horizontal　load,　the　traditional　m　method　would　underestimate　the　bending　moment　and　deformation　of　the　pile　element.　Therefore,　it　is　necessary　to　propose　relevant　calculation　methods　for　this　problem.　Simplifying　the　soft　ground　to　an　ideal　elastoplastic　body,　and　assume　that　there　exists　a　critical　point　at　a　certain　depth　of　the　ground　where　the　soil　mass　above　the　critical　point　behaves　plastically　and　the　soil　mass　below　the　point　behaves　elastically.　The　deflection　differential　control　equation　of　the　pile　is　established　and　a　simplified　elastoplastic　calculation　method　for　the　horizontally　loaded　single　pile　is　proposed.　The　results　of　field　measurements　and　parametric　study　show　that　the　maximum　bending　moment　calculated　by　the　simplified　elastoplastic　calculation　method　is　38.1%　more　accurate　to　field　measurement　in　comparison　with　the　traditional　m　method,　and　the　calculation　accuracy　of　the　maximum　horizontal　displacement　of　the　pile　is　improved　by　22.3%.　It　indicates　that　the　boundary　conditions　at　pile　top　have　significant　impact　on　the　distribution　of　lateral　deflection　and　bending　moment　along　the　pile.　Moreover,　parameters　of　soil　limit　resistance　and　soil　shape　have　remarkable　influence　on　the　maximum　bending　moment　and　lateral　deflection　and　it　is　recommended　to　choose　the　lower　values　in　pile　design.　©　2020,　Science　Press.　All　right　reserved.