A topology optimization design method for the thick plate transition structure was proposed. The optimization mathematical model was established in such a form that structure types were design variables, the deletion ratio of volume was constrain condition and the minimum structural flexibility was the objective function. Based on the strain energy criterion, the method of evolutionary structure optimization (ESO) was applied to achieve structural optimization model by deleting elements with low strain energy. Thick plates of various layout of shearing walls and columns subjected to vertical loads were studied, and then space truss model with strut and tie was obtained, which reflected the shortest path of the load transferring in thick plate. Furthermore, the behavior of the tie rod and strut bracing for the thick plate optimized was analyzed，and the formula of bearing capacity was deduced. The result has indicated that the proposed optimization design method is feasible.