In order to calculate the long-term deflection of steel-concrete composite girder accurately, on the basis of considering the shear deformation of composite girder, slip at the steel-concrete interface and shrinkage and creep of the concrete slab，the equilibrium differential equations for calculating the deflections of steel concrete composite girder are derived by using the energy variational method. By introducing the boundary conditions of simply supported and continuous composite girder under uniformly distributed load, the deflection calculation formulas can be obtained. The reliability of the calculation formulas are demonstrated by comparisons with experiments and with finite element analyses. The results show that maximum deflection of two span continuous composite girder considering shear deformation and interlayer slip the increases by 37.4% compared with the results from primary beam theory, and the deflection increases by 58% after considering the shrinkage and creep of concrete. The calculated maximum deflection of simply supported composite girder after considering the shrinkage and creep of concrete is 1.55 times larger than that of primary beam theory. It can be seen that shrinkage and creep can have a significant influence on the girder's deflection. The research results can provide theoretical basis for the long-term deflection calculation of steel-concrete composite girder.