This　paper　investigates　the　seismic　performance　of　exposed　RCFST　column--base　joints,　in　which　the　high--strength　steel　bars　(USD　685)　are　set　through　the　column　and　reinforced　concrete　foundation　without　any　base　plate　and　anchor　bolts.　Three　specimens　with　different　axial　force　ratios　(n　=　0,　0.25,　and　0.5)　were　tested　under　cyclic　loadings.　Finite　element　analysis　(FEA)　models　were　validated　in　the　basic　indexes　and　failure　mode.　The　hysteresis　behavior　of　the　exposed　RCFST　column-base　joints　was　studied　by　the　parametrical　analysis　including　six　parameters:　width　of　column　(D),　width--thickness　ratio　(D/t),　axial　force　ratio　(n),　shear--span　ratio　(L/D),　steel　tube　strength　(fy)　and　concrete　strength　(fc).　The　bending　moment　of　the　exposed　RCFST　column--base　joint　increased　with　D,　fy　and　fc.　But　the　D/t　and　L/D　play　a　little　effect　on　the　bending　capacity　of　the　new　column--base　joint.　Finally,　the　calculation　formula　is　proposed　to　assess　the　bending　moment　capacities,　and　the　accuracy　and　stability　of　the　formula　are　verified.