Horizontal　resistance　can　be　significantly　different　for　gravelly　soil　slope　sites　with　different　gradients.　The　impact　of　slope　gradient　on　the　horizontal　resistance　of　soil　based　on　a　three-dimensional　physical　simulation　test　has　been　investigated,　and　the　displacement　of　the　pile　top　and　soil　pressure　for　four　piles　under　various　gradients　(slope　gradient　0–45°)　was　analyzed.　The　research　reveals　that　①　The　soil　resistance　exhibits　a　linear　increase　stage,　non-linear　steep　increase　stage,　and　gradually　stabilizing　stage　with　the　increase　in　load.　②　The　ultimate　soil　resistance　is　significantly　affected　by　depth　and　displacement,　and　hyperbolic　variation　characteristics　related　to　the　displacement　stage.　It　has　a　slope　weakening　effect,　and　the　steeper　the　slope　gradient,　the　lower　the　ultimate　soil　resistance　of　the　pile　sides,　which　effect　is　negligible　when　the　depth　exceeds　0.6–0.7　times　that　of　the　pile　buried　depth.　③　Based　on　the　characteristics　of　horizontal　ultimate　resistance-displacement-depth　variation　in　soil,　a　gradient　factor,　which　is　only　related　to　the　slope　gradient,　was　used　to　describe　the　impact　of　gradient　on　the　soil　resistance　modulus　(kini)　and　ultimate　resistance　(pu).　kini　is　reduced　close　to　the　ground　surface　and　gradually　increases　with　depth　until　it　becomes　equal　to　the　value　of　level　ground.　The　ratio　between　pu　in　slope　ground　and　level　ground　was　determined　for　slope　angles.　The　above　horizontal　resistance　parameters　were　expressed　as　a　function　based　on　the　test　data　to　calculate　the　lateral　ultimate　bearing　capacity　of　gravelly　soil　considering　the　slope　gradient　factor.　The　research　results　developed　the　theory　of　foundation　design　for　building　structures,　promoting　the　reliability　evaluation　of　pile　soil　systems　towards　a　more　scientific　and　rigorous　direction.　©　2024　by　the　authors.