Abstract: The experiment of restrained CFST (concrete filled steel tube) dumbbell shaped members under torsion loads was carried out and the finite element model was established. The calculation formula of torsional bearing capacity of CFST dumbbell shaped cross section was derived. The results show that CFST dumbbell shaped members show good torsional elastic-plastic property. Increasing the width of web interspace can remarkably improve the torsional property for dumbbell shaped members, while the effects of changing height of web interspace can be negligible. The torsional bearing capacity of the CFST dumbbell shaped members can be considered as the sum of steel members (the upper and lower steel tubes and the steel webs), the concrete filled in the tubes and the concrete filled in the web interspace. The proportion of the concrete filled in the web interspace for torsional bearing capacity is less than 5% and thus its effects can be negligible. The derived and simplified formula can be used to calculate the torsional bearing capacity of the CFST dumbbell shaped members with more simplicity and accuracy.