In this paper, the frame structure of double cold-formed thin-walled C steel back to back connected with gusset plate was studied. The seismic behavior of three single-story and single-span frames was studied through both pseudo-static tests and finite element analysis. The hysteretic curves, skeleton curves and strain distribution were obtained by low cyclic loading. Two influencing factors, i.e. axial compression ratio and pitch of bolts, were also fully considered; the failure mechanism, bearing capacity, rigidity degradation, ductility and energy dissipation of the frames were carefully studied. The results revealed that all of the failure patterns of the frames indicated instability in load plane and local buckling at beam end and column base web. The axial compression ratio had greater impact on bearing capacity and rigidity degradation than the factor of bolt pitch. The ductility coefficient and energy dissipation of this structure accorded with the design requirements.