To study the durability of impermeable curtain and to propose suggestions for the strengthening grouting of the curtain in the later stage, physical-chemical analysis and permeability test are performed on the cement stone of the impermeable curtain which is constructed at the riverbed section of Danjiangkou dam in the early stage. The structures of hydration products of cement stone from core samples in most investigated holes are manifested to be compact with no abnormal mineral or chemical compositions. These core samples with compact structure exhibit good impermeability with little CaO corroded by percolating water. The corrosion speed of CaO reduced with the permeation time extended. The effective age of the curtains with dense cement stones is estimated to exceed 100 years, which indicates that the grouted cement curtain has good durability and corrosion resistance. Strengthening grouting is required at dam sections where CaO is visibly corroded.