The present study investigates the behavior of steel tubular columns in-filled with plain and steel fiber (SF) reinforced concrete. A nonlinear finite element model (FEM) using ANSYS program has been developed and the results obtained from the FEM are compared with the recent experimental works. The comparison indicated that the results of the model are evaluated to an acceptable limit of accuracy. The main parameters considered in the analysis were the slenderness, steel box wall thickness, cross section, percentage of (SF) and load eccentricity. The results indicated that the addition of SF in core concrete has considerable effect on the behavior of concrete-filled steel tube columns. A modified design equations have been implemented to (Euro code 4 2004) and (AISC/LRFD 2009) to consider the effect of SF reinforced concrete in the design of composite columns. A comparison study between the FEM results and those of the modified design equations is performed and good agreement is proved.