Abstract: To solve the problem of poor seismic performance of steel braced frame without floor in large industrial plants, the seismic performance and failure mechanism were studied through experiments and numerical simulations in this paper. The structural specimen was designed and manufactured with the scale of 1:4. Then, it was used to conduct the quasi-static test. A finite element model was established, and the feasibility was verified by analyzing and comparing with the test results. In view of the above, the influence of brace welding defects on both the bearing capacity and ductility of the frame was studied. At the same time, by increasing the stiffness of beam, the beneficial effects were analyzed. The collaborative work between the braces and frame was revealed. Suggestions for structural design were put forward.