Skewed box-section girder bridges are widely used in the proceeding of the road network construction. Ignoring the shear-lag effect will give rise to the instability and failure of bridges. The single-factor calculation theory of orthogonal box-section girder bridges cannot be applied to the calculation of the shear-lag effect of skewed box-section girder bridges. In this paper, simply-supported skew box-section girder bridge models with different widths of flanges were built by using the finite element software ANSYS. The distribution laws of shear-lag effect in the transverse and vertical of skewed box-section girder bridges were more obvious with an increase in the flange width.