Abstract: Dalongtan hydropower station is located in one carbonate rock area. The karsts are controlled by lithologic characters and structural features as follows: 1)the lithology in the first member of Najinguan formation of Ordovician（O1n1）,the first layer of the second member of Najinguan formation(O1n2-1)and the second layer of the fourth member of the Cambrian(4-23m)are shale infiltrated limestone,band argillaceous limestone and band siliceous limestone respectively. The karts in these rocks are very weak and oppositely strong in other rock layers; 2)Karsts develop along the bedding surface and fault plane,which form karst canals. So the seepage mainly occurs along these karst faults. In antiseepage curtaindesigning,the design relies on the shale of 188 m depth and emphasizes the locations of the faults. Results of the longterm groundwater observation and analysis show that the efficiency of the antiseepage curtain is very good and there is no large seepage. Only at the sites where the faults pass,the amount of seepage may be somewhat larger. The achievement of the antiseepage curtaindesigning in Dalongtan hydropower station gives a good example and may provide significant reference for other projects