This　paper　proposed　a　uniaxial　stress-strain　relation　model　of　core　Reactive　Powder　Concrete　(RPC)　for　reactive　powder　concrete　filled-steel　tube　(RPCFST),　which　is　applicable　for　RPC,　especially　for　RPC　confined　by　external　steel　tube.　To　validate　the　constitutive　law　model　proposed,　20　specimens　of　RPCFST　were　prepared　and　tested　under　eccentric　loading.　Due　to　the　limitations　of　experimental　apparatus　and　ambient　conditions,　some　significant　characteristics　of　RPC　and　RPCFST　are　not　able　to　measure　and　reveal　only　by　experiments.　To　solve　this　problem,　the　stress　strain　relation　model　proposed　was　applied　to　develop　a　finite　element　model　for　the　behavior　of　RPCFST　members　under　eccentric　loading　in　details.　The　performances　of　RPCFST　were　analyzed　and　tracked　through　simulation　of　the　FEM　model.　The　results　show　that　the　stress　strain　relation　model　of　core　RPC　and　FEM　model　developed　are　applicable　and　effective.