Abstract: 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.