Composite box girder with corrugated steel webs has small torsional stiffness and is easy to produce warping deformation. To reasonably calculate the shear stress of single-box multi-cell composite box girders with corrugated steel webs under restrained torsion， the shear flow was decomposed， and constants that can reflect the shear flow transfer mechanism of each cell box wall were introduced based on the shear flow transfer path， longitudinal equilibrium of differential bodies and warping displacement continuity. The practical formulas for section geometrical property and shear stress considering the folding effect of corrugated steel web were deduced. The governing differential equation for analyzing restrained torsion was established based on Reissner’s principle， and an analytical solution was obtained by employing the initial parameter method. The torsional shear stress of the simply supported box girder under an eccentric loading was calculated by the present analytical method and ANSYS finite element method. The shear stress increment coefficient reflecting the effect of torsional shear stress on total shear stress and the shear stress coefficient reflecting the contribution degree of the warping shear stress to the total shear stress were introduced. The influences of girder width and cell number on the shear stress were analyzed. The results show that the present analytical solution agrees well with ANSYS finite element solution. The increase in girder width and cell number can reduce torsional shear stress. The shear stress increment coefficient of the outside web under restrained torsion reaches 1.69， and the total shear stress distribution between webs shows obviously uneven. The influence of warping shear stress on torsional shear stress can’t be ignored. The effect of torsional shear stress on principal tensile stress in the top and bottom concrete slab should be considered in the design to avoid oblique cracks.