Abstract: The paper analyses the styles and reasons of the break in the concrete dams. Main reasons of four breaking styles (freeze-thaw, frozen heaving,cracks,corrosion and cavitation erosion) prove to be low grade of concrte strength,low resistance to freeze-thaw,low resistance to permeation,high temperature stress,and material selected and construction out of control. The paper introduces the repairing technique and the selection of repairing materals elaborately,according to the repairing practices of some concrete dams, such as Fengman, Yunfeng, Huanren,Shenwo and etc..