Test results of variable cross-sectional concrete filled steel tubular (CFST) laced columns on axial load indicate that the ultimate load of specimens reduces gradually with the increase of column length and the decrease of slope of longitudinal elements. Following this rule, a calculation method of the ultimate load carrying capacity of CFST variable cross-sectional laced columns on axial load was studied on the base of calculation frame of equal cross-sectional CFST laced columns. A method by using equivalent length to calculate equivalent slenderness ratio and stability factor of variable cross-sectional CFST laced columns was presented. The calculation results of specimens' ultimate load by this method are coincident well with the test results. Finally, a rational and applied method to calculate the ultimate load carrying capacity of four-element variable cross-sectional CFST laced columns was presented on the base of numerical results from FEM analysis, and it's hoped to provide reference for the further perfection of CFST design criteria.