Abstract: Based on previous experimental researches, the twin shear unified strength theory is adopted, in which the influence of intermediate principal stress R2 is considered, and it is applied to various materials of different performance in tension and compression under complex stress state. The reason that the bearing capacity under ax ial compression is enhanced is analyzed, and the formula of bearing capacity under axial compression that had been established is modified. Research results show that, comparing the calculated values of the formula for bearing capacity under ax ial compression based on the twin shear unified strength theory and the values of the previous formula, the former are more closed to the experimental values, and can provide more accurate and economic results for practical engineering; the unified strength theory can be well applied to the theoretical calculation in multi-ribbed slab structure.