Sandwich composite panel is a new developed building material applied in steel residential houses, but the theory and experiment of this panel is still limited. In order to study the influence of the boundary conditions and shear connector patterns on flexural behavior of the panels, two groups of panels were cast and tested. Failure modes of the test panels under the uniformed transverse load, load-deformation response, strains in two concrete wythes, crack loads and ultimate load-bearing capacity were recorded and analysed. Test results showed that different angles and distances of plane truss shear connectors affected the ultimate flexural strengths significantly. The strain curves of two concrete wythes revealed that the plane truss shear connectors of panels worked well to make the two wythes act as a solid slab. It is concluded that the sandwich composite panel is available in steel residential houses because of its economical and high flexural strength.