Structural system composed of high-strength steel frame with energy-dissipation elements is one of the suitable solutions for damage tolerant structures. The main structure is normally designed in elastic zone for design earthquake level; however, there are still some risks to step into plastic zone in maximum considered earthquake levels. Because of high strength steel having high yield ratio, it is concerned to fracture early after yielding. In this paper, mock-up cyclic-loading tests of 800Mpa steel beam-column frame with diagonal BRBs are carried out until their fracture of BRBs and beam-column connections. Their fracture mechanism is investigated using detailed analyses, and estimation method for their cumulative energy dissipation capacities is proposed.