This paper introduces a new connection－inner and through-type diaphragm, which is recommended by Technical Specification for Structures with Concrete-filled Rectangular Steel Tube Members. It studies some factors including the additional plates installed on both sides of the flanges, the width-to-thickness ratio of the column and the length of the through diaphragm which have an influence to the seismic resistance behaviors of connection through cyclic test. The results show the hysteresis curves attained in the experiment are full and the rigidity deterioration is not obvious. The connection models have a good energy dissipation capacity. Meanwhile the stress distributing can be ameliorated and the ductility of the connections can also be improved through welding the additional plates to both sides of the flanges.