Corrugated steel web bridge has been incorporated as a new kind of bridge structure recently in China. The single cell and single box section is regularly adopted, while the multi-cells and single box section is not, and its cross section shear force distribution rules are not yet clear. This paper presents research findings on corrugated steel webs shear force distribution of three-box single cross section girder bridges. A detailed three-dimensional finite element model of a three-box single cross section girder bridge with variable depth was established using Midas/Civil software. The shear force distribution ratios of critical structural components, such as top plate, web and bottom plate, and those between different webs were analyzed, especially for the worst scenario, the largest cantilever construction state. The results show that corrugated steel webs take a proportion of 35% to 65% shearing force of three-box single cross section girder bridges with variable depth, which is lower than 80% for constant depth girder bridges. Bottom plate profile change is identified as the main reason to cause the decreasing of web shear force distribution.