Abstract: Based on the analysis of test results of 233 specimens, this paper further demonstrates that confinement index is a factor in ultimate loading capacity. Empirical calculation formulas for ultimate loading capacity, peak strain, remaining strength and stress-strain curves of composite material of concrete filled tubular steel(CFTS)stub columns are established for cubic compressive strength of concrete ranging from 20 to 110MPa. The results show good agreement with experimental data. The present work can be used as reference for non-linear finite element analysis of CFTS columns.