Abstract: According to damage criteria based on strength of extension, it establishes the masonry constitutive model and 3D finite element numerical model,analyzes the stress and deformation of Nanhu reservoir masonry gravity dam of Hui country in Henan under three working conditions： ordinary water level,designed flood level and check flood level.It concludes that under different working conditions, this gravity dam stress condition vary in the norm allowed band.The bank slope section needs more monitoring measures because of the easily appearing tensile stress.