Abstract: Global stability of the beam with reduced beam section (RBS) connections in steel frames is analyzed. The global stability of the RBS beam under different loads is studied using energy method; with the stiffness of the reduced region replaced by the equivalent reduced stiffness, the critical load of the RBS steel beam is obtained and compared with that of the ordinary steel beam. The variation of the critical moment of the RBS beam with cut dimensions is discussed, and the effects of cut parameters on the critical moment of RBS beam flexural-torsional buckling are verified by the finite element method. The results show that reductions have great effect on RBS beam flexural-torsional buckling, and the critical moment decreases obviously compared with that of the ordinary beam, so adverse effect should be considered in engineering design. The effect of beam cut section on beam stiffness decreases as the beam span increases, so the effect of cut dimensions on the critical moment of RBS beam can be neglected when the ratio of beam height and span is small.