An analytical solution is launched for Twin-cell Composite Box Beam (TCCBB) considering the impact of shear lag effects of concrete slab and twin-cell steel girder. To in-depth explore its mechanical mechanism, a new warping displacement mode of wide flange is chosen to meet the essential deformation feature of this TCCBB model by authors. Combining the virtual work principle with the thin-walled beam theory, its governing equations and boundary conditions are established for the TCCBB model. Closed form solutions for longitudinal strain and its shear lag coefficients are also derived under concentrated loads. What's more, experiment investigation and related parameter impact analysis are carried out for this established TCCBB model. Through this research, it shows that the proposed method can be applied to describe and predict shear lag behaviors for this type of composite structure. That further suggests that it provides a certain reference value for engineering design and its late reinforcement and maintenance in the composite structure.
