To understand the performance of buckling-restrained brace (BRB) as a lateral-force resisting component, an assembled all-steel double-core BRB was designed, and its bearing and energy dissipation capacities was studied through quasi-static experiments. Firstly, a single-core BRB specimen was tested to find any design and anchorage deficiencies, and after improvement, the load-displacement curves and low-cycle fatigue curves were successfully obtained for other single- or double-core specimens, and the design parameters of the BRBs, such as strength, deformation, and energy dissipation, etc., were obtained after studying the characteristics and laws of the curves. Furthermore, numerical simulations were conducted on BRBs using Bouc-Wen model under earthquake excitations. The test and analysis results show that BRBs overcome the deficiencies of the traditional braces which tend to buckle under compression. The hysteretic curves are basically symmetric for compression and tension, in full spindle shape, with high damping ratios, and endure fatigue well under reciprocal loads. The hysteretic properties can be simulated well by Bouc-Wen model. The proposed double core steel BRBs have stable performance and are east to assemble, and are suitable for practical engineering application.