The　out-of-plane　mechanical　behavior　of　a　dumbbell-shaped　CFST　arch　under　spatial　loads　has　been　experimentally　investigated.　The　experiment　results　were　compared　with　those　of　the　out-of-plane　test　of　a　single　tube　CFST　arch.　Based　on　the　FEM　model　which　was　verified　by　test,　the　parameter　analysis　of　the　out-of-plane　ultimate　bearing　capacity　was　discussed.　The　results　show　that　the　model　arch　was　mainly　bearing　in-plane　compression,　and　that　in　the　out-of-plane　direction　was　bearing　out-of-plane　bending　moments　at　the　arch　crown.　The　failure　mode　of　the　arch　was　its　out-of-plane　instability　finally　when　the　crown　and　springing　were　in　plastic　states.　In　the　mechanics　behavior　of　a　model　arch,　the　proportion　of　out-of-plane　bending　was　the　maximum,　which　reached　71%~78%.　The　out-of-plane　ultimate　bearing　capacity　was　less　than　that　of　in-plane　ultimate　bearing　capacity.　The　decline　range　was　related　to　the　rate　of　in-plane　load　to　out-of-plane　load,　the　out-of-plane　rigidity　of　the　arch,　and　the　cross　section　type.　With　the　increasing　height　or　the　width　of　flank,　the　rigidity　of　dumbbell　section　and　out-of-plane　ultimate　bearing　capacity　were　increasing.　When　the　height　increased　33%　or　width　increased　50%,　the　out-of-plane　ultimate　bearing　capacity　increased　11%~17%　or　10%~14%.　The　most　important　parameter　which　influences　the　out-of-plane　ultimate　bearing　capacity　was　the　out-of-plane　rigidity.　The　rate　of　buckling　loads　to　ultimate　bearing　capacity　showed　that　the　buckling　coefficient　greater　than　4　was　safe　for　dumbbell-shaped　CFST　arch　bridges　in　practice.　©　2015,　Engineering　Mechanics　Press.　All　right　reserved.