Abstract: This paper studies cooperative behaviors of steel and concrete in a hollow-concrete-filled steel tube (H-CFST) under an axial loading. Based on the experiments, the formula of composite standard compressive strength was suggested. The derivation of composite reliability of H-CFST member analyses was acquired by the bearing capacity proportion of steel and concrete. According to the experimental results, the composite reliability index of H-CFST members was developed. Therefore, the coefficient of strength reduction is suggested by means of the Naional Standard.