Lateral　stiffness　is　a　basic　component　property　in　the　design　of　a　tall　pier.　To　investigate　the　effects　of　axial　compression　ratio　and　relative　height　to　thickness　ratio　of　a　low-yield-point　(LYP)　steel　plate　on　the　lateral　stiffness　of　an　innovative　tall　pier　with　rectangular　concrete-filled　steel　tubular　(CFST)　columns　and　a　replaceable　LYP　steel　plate　composite　box　section,　quasi-static　cyclic　tests　were　conducted　on　four　tall　pier　specimens.　The　preliminary　test　results　indicate　that　the　specimens　with　composite　box　sections　have　sufficient　initial　lateral　stiffness　to　meet　the　displacement　limit　requirement　at　the　top　of　the　tall　piers　during　the　elastic　stage,　and　the　lateral　stiffness　might　decrease　by　32%-53%　when　clastic-plastic　buckling　occurs　in　the　LYP　steel　plates.　Furthermore,　extensive　parametric　analyses　were　conducted　to　explore　the　influence　of　the　key　factors　on　the　lateral　stiffness　of　the　tall　piers　with　composite　box　sections　by　verified　finite　element　models.　The　parametric　analysis　shows　that　axial　compression　ratio　and　both　relative　height-thickness　ratio　and　yield　strength　of　the　LYP　steel　plate　have　little　effect　on　the　initial　elastic　lateral　stiffness;　the　post-buckling　lateral　stiffness　is　closely　related　to　the　relative　height-thickness　ratio　of　the　LYP　steel　plate:　when　the　relative　height　to　thickness　ratio　decreases　from　200　to　100,　the　buckling　and　the　minimum　lateral　stiffnesses　increase　by　37%　and　48%,　respectively.　By　simplifying　the　tall　pier　with　a　composite　box　section　as　that　with　multiple　CFST　columns　linked　by　LYP　steel　plates,　the　practical　formulas　for　the　initial　elastic　and　buckling　lateral　stiffnesses　were　established,　respectively.　The　theoretical　calculation　results　agree　well　with　the　experimental　and　numerical　results,　and　the　latter　can　be　used　to　estimate　the　minimum　lateral　stiffness　of　the　tall　pier　with　medium　or　thick　LYP　steel　plates　after　a　severe　earthquake　ground　motion　input.　©　2024　Chang＇an　University.　All　rights　reserved.