【原文】A buckling-restrained brace with a flat energy dissipation element, a building with the brace and an assembly method of the brace belongs to the field of force-resisting members of structural engineering. The brace includes a telescopic inner restrained member, an outer restrained member sleeved outside the inner restrained member, and the flat energy dissipation element between the inner and outer restrained members; the inner restrained member includes a first and a second steel square tube which are connected; the flat energy dissipation element includes four flat fuses, and two ends of each fuse are connected to four sides of the first and second steel square tube by bolts; and the inner section of the outer restrained member is square, the outer restrained member covers the flat energy dissipation element, and a certain gap is disposed between the outer restrained member and the flat energy dissipation element.