In this paper a numerical model for fire resistance analysis of bar-reinforced concrete filled steel columns with square and circular cross-sections have been put forward. The model has been validated by testing results. There is a good agreement. Used of the theoretical model, the relations between the fire resistance and various parameters have been analyzed. On the basis of that, formulas for the calculation of the fire resistance of bar-reinforced concrete filled square and circular steel columns under ISO-834 Standard Fire Curves are developed respectively. The calculated results have a good agreement with those of mechanic model and test.