In order to study the normal section bearing capacity and the formation requirements of a novel inverted U-shaped steel-encased concrete composite beam, the nonlinear finite element models of the composite continuous beams have been established based on the existing U-shaped steel-encased concrete composite continuous beams. The load-deflection curve at mid-span of the composite continuous beam finite element model was plotted, and compared with other test results. It proves the rationality and effectiveness of the modeling method and parameter selection of the composite beam finite element models. Using the established finite element model of composite continuous beams, the main influential parameters of normal section bearing capacity of the inverted steel-encased concrete composite beams are analyzed. Based on the test and simulation results of normal section bearing capacity of inverted U-shaped steel-encased concrete composite continuous beams, it is proposed that when the normal section bearing capacity of the composite beam is calculated by the simplified plastic theory, the plastic theoretical calculation value of the normal section bearing capacity of the composite beam should be multiplied by a correction factor of 0.96. Comparing the calculated value of 0.96 times the plastic theoretical calculation value of the normal section bending capacity of the composite beam with the calculated value of the finite element model of the composite beam, the two values are found very close in safe side. The proposed modified simplified plastic theory calculation value of the normal section bending capacity of the composite beam is accurate and reliable enough.