The　bearing　capacity　of　pile　under　horizontal　load　is　not　only　related　to　pile　size　and　pile　material,　but　also　closely　related　to　soil　parameters.　In　this　paper,　based　on　the　probability　analysis　method　of　random　field　theory,　a　non-stationary　random　field　model　is　firstly　proposed　for　the　undrained　shear　strength　Su　of　soil.　In　this　model,　the　uncertainty　of　the　increase　trend　of　Su　along　the　direction　of　depth　is　taken　into　account,　and　the　mean　value　and　standard　deviation　of　random　field　increase　linearly　along　the　depth.　Then,　by　comparing　with　other　random　field　models,　the　applicability　of　the　non-stationary　random　field　model　for　undrained　shear　strength　proposed　in　this　paper　is　verified.　Finally,　the　random　field　model　is　applied　to　the　reliability　evaluation　of　horizontally　loaded　pile,　and　the　influence　of　the　spatial　variability　of　undrained　shear　strength　on　the　failure　probability　of　horizontally　loaded　pile　is　discussed.　The　results　show　that　the　coefficient　of　variation　and　correlation　length　of　undrained　shear　strength　have　obvious　influence　on　the　failure　probability　of　pile　foundation.　The　uncertainty　of　increase　rate　b　of　undrained　shear　strength　with　depth　also　has　influence　on　the　failure　probability　of　pile　foundation.　If　the　spatial　variability　of　the　soil　parameters　is　not　considered　in　the　evaluation　and　design　of　pile　foundation,　the　failure　probability　of　pile　foundation　will　be　large,　which　will　make　the　design　results　of　pile　biased　toward　conservative.