Concrete-filled hollow steel tubular (CFHST) columns have become appropriate solution for the construction of offshore platform supports, columns for large industrial workshops, as well as high rise buildings. In this research, a numerical study was conducted to investigate the optimal design of the CFHST columns. The numerical study comprises two phases: verification of experimental work using a nonlinear finite element software ANSYS 18.1 and a parametric study on the behavior of 33 full-scale CFHST columns. The cross-sectional shape, the depth to width (ts/bs) ratio, the slenderness ratio, and the distribution of the total steel area through the concrete core and the steel tube were the main variables. The reinforcement of the concrete core as well as the confinement of the external steel tube enhanced the ultimate loads, stiffness, and ductility of the CFHST columns. The Use of 4% internal longitudinal steel reinforcements for the CFHST columns results in up to 30 % increase for the values of the ultimate loads.