Shear mechanism of the cross bore slab of tubular hollow slab on cast-in-place concrete is set forth. Shear force and normal stress are calculated for each section of cross bore slab of tubular hollow slab with supported in one-way direction. We can put forward suggestions based on the three conditions. One condition is that shearing stress is no more than shearing resistance on cross bore slab. Another is that tensile stress on rib of cross bore slab is no more than tensile strength of the concrete. The last one is that concrete shearing stress on rib of parallel bore slab is less than its shearing resistant strength. Meanwhile one example is given. So that we can obtain the requirements for minimum rib between bores of tubular hollow slab.