In this study, based on the degenerated shell element theory, the displacement field of the element is deduced, and the nonlinear composite element mode of the reinforced concrete multi-T beam is established. The longitudinal carrying bar is treated by the space bar element and its contribution to the stiffness matrix of nonlinear composite elements is deduced. The material nonlinearity of concrete is considered by the four parameters’ Ottosen criterion, and the geometrical nonlinearity of the structure is taken into account by the V. Karman assumption to analyze the influence of geometrical nonlinearity on the structure. The typical example shows that the nonlinear combination element of reinforced concrete multi-T beam with double nonlinearities is in good agreement with the experimental data. The element can be used to correctly analyze the structure nonlinearity. When the partial load is loaded, the stress of the reinforced bar on the side beam develops more rapidly and reaches the yield stress firstly, while the stress of rest reinforced beams of all the main girders develops in sequence until the structure is destroyed. For reinforced concrete multi T beams, the effect of material nonlinear is evident, and geometrically nonlinear effect can be excluded within a certain range.