To design concrete encased steel column (SRC) structures more reasonably and more economically, it is necessary to appropriately evaluate the seismic resistance capacity of SRC members. In this study, a mehtod to calculate ductility, especially plastic deformation capacity, of SRC members was investigated analytically and statistically. Based on the study results, we introduced a comparatively accurate calculation method. Additional tests were also carried out and the applicability of the calculation method was investigated. Finally, a hysteresis model of SRC members was investigated by using the results of cyclic loading tests.