A　finite　element　model　was　developed　and　a　formula　for　the　torsional　stiffness　of　the　concrete　filled　steel　tubular　(CFST)　dumbbell-shaped　cross　section　was　derived.　It　shows　that　the　torsional　stiffness　of　the　CFST　dumbbell-shaped　cross　section　can　be　considered　as　the　sum　of　the　torsional　stiffnesses　of　the　steel　members　(the　upper　and　lower　steel　tubes　and　steel　webs),　concrete　filled　in　the　tubes,　and　concrete　filled　in　the　web　interspace.　However,　the　volume　of　concrete　filled　in　the　web　interspace　accounts　for　only　a　proportion　of　less　than　5%,　hence　its　effect　is　negligible,　and　the　formula　has　been　simplified.　Comparison　between　the　calculation　results　and　the　finite　element　modeling　results　shows　that　the　proposed　formula　in　this　study　is　a　convenient　and　accurate　method　for　the　estimation　of　torsional　stiffness　of　a　CFST　dumbbell-shaped　cross　section.