Abstract: To study the internal structure of rocking column used in offshore platform, 10 Concrete Filled Steel Tubular ( CFST) column specimens subjected to three-point bending test were tested, including concrete filled round steel tube, concrete filled round steel tube with inner I-cross section, concrete filled round steel tube with inner circular cross section, concrete filled square steel pipe, concrete filled square steel tube with inner I-cross section, concrete filled square steel tubes with inner cylindrical cross section. Failure process, failure modes, the bearing capacity and deformation capacity of CFST columns were studied considering different shapes and different section forms, and the internal changes and mechanical characteristics of specimens were analyzed which were loaded by local transverse-longitudinal ratio and the local strain. The test results show that when specimens are in the process of loading, steel tubular and concrete as well as internal different cross-section steel have different mechanical characteristics and collaborative work mechanisms at different loading stages. Circular CFSTs have better ferrule effects which can enhance the bearing capacity and deformation capacity of specimens;the CFSTs with two cylindrical cross sections have the best shear performances.