Abstract: Based on the theory of circumferential non-deformation, and combined with the calculation and analysis on constrained torsion of closed thin-wall members, the distribution and calculation of torsional shear stresses were addressed for composite box girders with corrugated steel webs. The distributions of free torsional shear stresses and warping torsional shear stresses were further demonstrated through deduction of the formula for calculating the shear flow of cantilever plates in restrained torsion. The relevant shortcomings in calculating shear stresses by existing references were pointed out. A simply supported composite box girder with corrugated steel webs was taken as an example to compare the analytical results with those from the ANSYS finite element method. The results show that, in the sections of box girders with corrugated steel webs, the torsional shear stresses are mainly undertaken by corrugated steel webs, then by concrete bottom plates. The maximum shear stress in the bottom plate occurs at its center and is almost half that in the webs. The torsional shear stresses in the top concrete plate and the cantilever plate are very small. The calculated results of torsional shear stresses are consistent with those with the finite element method on the whole. The shear stress is zero at the free tip of the cantilever plate and gradually increases and reaches the peak value with the distance away from the tip end.