Basing on the buckling-restrained braced frame under severe earthquakes, and from the point of additional effective damping ratio and energy principle, a simplified calculation method to solving elastic-plastic displacement of the buckling-restrained braced frame under severe earthquakes has been systematically analyzed. In this paper, the detailed calculating method and steps are presented. Moreover, the comparing analysis between the calculation result of simplified calculation method and the mean of the results of ten seismic waves’ elastoplastic time-history analysis has been carried out. The outcome shows that the simplified calculation method is an exact and valid method.