In order to study the seismic performance of steel structure in China and look for the constitutive relationship of steel under cyclic loading, a variety of loading was imposed on total 50 specimens of Q235B and Q345B steel and their monotonic behavior, hysteretic behavior, macro and micro failure modes, ductility characteristics and cumulative damage degradation were investigated; Ramberg Osgood model was used to fit the curve of cyclic loading and then the one dimensional stress strain skeleton curves of Q235B and Q345B under cyclic loading were obtained; based on the Chaboche plastic constitutive model for steel, two material parameters of constitutive models were obtained from experimental data calibrated with ABAQUS which provided an important basis to accurately calculate the response of future structures under earthquake. The results show that the response of steel under cyclic loading and the monotonic loading are quite different, therefore, the skeleton curve under cyclic loading plays an important role for accurate numerical simulation; cyclic loops and amplitudes seriously affect the fracture ductility of specimens and the failure strain under cyclic loading cannot be determined in accordance with the monotonic loading.