Abstract: This paper presents a complete differential equation for the plastic bifurcation buckling of plates under combined loadings. The analysis is based on the Prandtl-Reuss incremental theory and the Mises yield criterion. Using the resolving techniques of eigenvalues author analyzes the simply-supported rectangular plates subjected to compression in two perpendicular directions and shear loadings; hence the parameters of plastic stability are obtained and the plastic bifurcation stress curves are drawn in the plastic flow range and the strain hardening range. Analyzing results show good correlations with theoretical results.