Abstract: ： The stress and displacement of a steel plate deep-beam (SPDB) under horizontal loads are predicted by establishing a mechanical model and applying a semi-inverse method in elastic mechanics. The analytical formulas for the stress components and displacement components of SPDB were derived. Experimental results show that the calculation with the formulas could meet the requirements of accuracy. For the SPDB with both sides stiffening ribs, the stress distribution varies as the stiffener-plate area ratio changes. When the stiffener-plate area ratio is zero, the solution of SPDB is equal to that of a non-stiffened one. The normal stress of SPDB declines with increasing stiffener-plate area ratios until an approximately pure shear condition occurs. The solution provides a theoretical foundation for steel component design and stability analysis.