Abstract: Taking slenderness ratio and eccentricity ratio as the principal factors，static behavior of 24 pieces of concrete filled square steel tubular beam-columns strengthened by CFＲP externally ( S-CF-CFＲP-ST ) were experimentally investigated． The test results showed that the axial load-deflection curves on the cross-section at midheight of the composite members could be divided into elastic stage，elasto-plastic stage and softening stage． Analysis on the experimental results showed that the steel tube and its outer CFＲP material could cooperate both longitudinally and transversely，in addition，deflection curves of the tested members behaved much similarly as half sinusoidal curve． The failure modes and the axial load-deflection curves on the cross-section at mid-height of the specimens were simulated by using ABAQUS software． The simulated results agreed well with experimental values．