Abstract: A method for calculating the deflection of composite beams with web openings is described. The effective width of concrete slab working in bending resistance in the top section of perforated segment is proposed and fitted. By combining shear deformation and bending deformation of Vierendeel members into equivalent shear deformation, the equivalent shear rigidity of a perforated segment is obtained. Observed the phenomenon that a perforated segment and an unperforated segment have different section rigidities, a segmented beam element model is established to solve the deflection calculation formulas by traditional beam theory. The formulas show an excellent agreement with the results of finite element analysis using solid and shell elements.