Abstract: Based on the twin shear unified yield criterion, the plastic limit loads of simply supported circular plate under uniform annular load are given. The other available solutions based on Tresca criterion, Mises criterion and twin shear stress criterion are special cases or approximations of the present result. The present solution is suitable for many materials with same strength in tension and in compression. The plastic limit loads of simply supported circular plates under various loads can be obtained based on the present solution.