The tensile capacity of a high-strength bolt,determined by the bolt itself and the steel plate respectively is introduced, the effect of bolt hole is considered. The required thickness of extended unstiffened end-plate is presented, and the weak-end-plate and strong tensile high-strength bolt requirement for seismic design is discussed. A correct plastic mechanism, in which 1/4 elliptical conical plastic surface is included, is used to determine the thickness of stiffened end-plate. The thickness by the new equation is found to be 4~10% thicker than by the equation in GB 51022-2015. The thickness of the stiffened end plate is found to be about 0.75 times the thickness of the unstiffened end plate.