In　the　design　and　analysis　of　pile　foundations,　the　horizontal　load　is　an　important　factor　that　needs　to　be　considered.　The　reliability　analysis　can　take　the　uncertainty　of　various　parameters　into　consideration　and　thus　reduce　the　design　deviations,　especially　the　uncertainty　of　soil　parameters.　This　paper　proposes　a　reliability　analysis　method　considering　the　spatial　variability　of　soil　for　the　horizontally　loaded　pile.　Firstly,　a　parameter　sensitivity　analysis　was　performed　by　the　Sobol　sensitivity　method,　and　the　critical　variables,　including　the　undrained　shear　strength　C-u,　the　soil　strain　epsilon(50),　which　represents　the　soil　strain　when　principal　stress　difference　reaches　half　(50%)　of　the　maximum　value　in　triaxial　test,　and　the　horizontal　load　and　applied　moment,　are　identified　and　taken　as　the　random　variables.　Moreover,　the　spatial　variability　of　soil　parameters　(C-u　and　epsilon(50))　are　simulated　as　one-dimensional　random　field　through　the　orthogonal　series　expansion　method.　The　failure　probabilities　of　pile　foundation　under　the　failure　modes　of　deflection　and　strength　are　evaluated　by　Monte　Carlo　simulation.　Finally,　the　proposed　method　is　verified　through　case　study　in　which　the　influences　of　the　spatial　variability　of　soil　parameters,　the　uncertainty　of　the　horizontal　load　on　the　failure　probability　were　investigated.　The　results　show　that　the　uncertainty　of　horizontal　loads　and　C-u　make　significant　effects　on　the　reliability　of　pile　foundations.　The　increase　of　correlation　length　of　C-u　and　epsilon(50)　will　lead　to　the　increase　of　the　mean　value　of　pile　response,　which　has　different　effects　on　the　failure　probability　under　different　failure　modes.