Abstract: This study proposes an analytical model taking into account slip and shear-lag effects of a steel-concrete composite box beam. This model introduces five variables, which include vertical displacement, axial displacements as well as warping intensity functions of a concrete slab and a steel beam. Balance differential equations are deduced by the virtual work theorem for three-dimensional bodies. The finite difference method is utilized to obtain numerical solutions of the equations. The interface slip and shear-lag effects of a simply supported and a two-span continuous composite box-girder bridges are then analyzed by utilizing the proposed analytical model and FE elaborate model. The correctness and applicability of the proposed analytical model are verified through a good correlation between the results from two models. Finally, based on a simply supported composite box-girder bridge under a vertical uniform load, some analysis on the functions and advantages of the proposed analytical model are conducted. The influences on shear-lag effect of the arrangement of the prestressing tendon and beam-column effect from an axial-bending load are analyzed. Three advantages of the proposed analytical model are explained by comparing with the analytical models from previous study.