The horizontal bearing characteristics and reliability of the bridge foundation piles in the sloping ground are affected by the slope effect and parameter uncertainty. Considering the slope effect，a simplified model of the pile was first established and the finite difference solution of internal force analysis was derived. Based on the sto? chastic response surface method，the limit state function was proposed to analyze the horizontal bearing reliability of piles in sloping ground. The first order second-moment calculation method was used to solve the reliability index and failure probability，and the calculation results were compared with the Monte Carlo method and quadratic function re? sponse surface method to verify the rationality of the solution method and program. Finally，the influences of pile di? ameter，proportional coefficient of foundation resistance，elastic modulus of pile body and horizontal load on the hori? zontal bearing reliability of piles were discussed with the engineering example. The results show that the variability of pile diameter has the greatest influence on the horizontal bearing reliability of piles under the failure mode of horizon? tal displacement. The failure probability of foundation piles increases with the increase of slope effect reduction fac? tor. The slope effect and parameter variability have little influence on the failure probability of piles under the failure mode of materials yield. For bridge high pier pile located in the sloping ground，the deformation safety should be in? creased to ensure the reliability of the pile.