Abstract: The mechanical behavior of the steel-concrete composite beam of a cable-stayed bridge is different from that of conventional composite beams. A segment model with an enlarged scale of 1:2 was designed and established based on the real steel-concrete composite beam of Guanyinyan Yangtze River Bridge. The test for both individual load case and combined load case of an ultimate limit state were carried out to obtain the distribution of the stress and deformation of key sections. The mechanical behavior of the steel-concrete composite beam was also studied by finite element analysis. The results show that when the composite beam is subject to a large bending moment the strain distribution of the cross section is nonlinear, implying that the plane section assumption is not suitable in this case. The relative slippage between a steel beam and a concrete slab caused by the bending moment can be significantly reduced by the axial force, which is much smaller compared with the common composite beams. The finite analysis results match well with the results by the model test and meet the engineering requirements as well. The majority of the axial force is born by concrete slabs, while the moment is mainly undertaken by steel girders.