Abstract: Based on the analysis of stress and bending moment distribution of rotationally symmetrical circular plates in plastic limit state, a generalized twin shear unified yield condition in terms of bending moments is developed in the context of twin-shear unified strength theory. The generalized twin shear unified yield condition is a symmetric folded line, convex outward and closed. It can be applied to the plastic limit analysis of circular and annular plates, and the materials can have any tensile to compression strength ratio and any shear to compression strength ratio. The plastic limit states of simply supported and clamped circular plates are analyzed. Their ultimate loads, moment fields and velocity fields in plastic limit states are obtained. The ultimate loads varied with the tensile to compress strength ratio α and the media shear stress factor b. Their influences are analyzed.