Abstract: The simplified mechanical model for skew box girder is established. Assuming the temperature gradient of sunshine is described by exponential curve or broken lines, the analytic expressions of primary and secondary internal forces are derived for single-span and multiple-span continuous skew box girder. The influences of skew angle and the ratio of bending stiffness to torsion stiffness on the secondary internal forces are studied and presented through curves and diagrams. It is found that large secondary bending and torque moments occur in both the multiple-span continuous and single-span skew box girders. The ratio of bending stiffness to torsion stiffness and skew angle affect significantly the secondary internal forces, especially for the case of smaller ratio of bending stiffness to torsion stiffness. When skew angle reaches 90°, the secondary bending moment is distributed uniformly along the beam length and is numerically equal to the primary bending moment, but is opposite in direction.