Abstract: In order to solve the problem of water supply for the Funing County and irrigation of the surrounding rural farmlands, a reservoir is built by plugging the Qinghuadong underground river. The designed capacity of the reservoir is 99.34 million cubic meters, blocking body is 87.5 m in height, and the largest impoundment depth is about 116 m. Geological survey proves that there are relatively complete relative-impermeable strata and impermeable strata around the reservoir basin, and the elevation of all spring outcrops is higher than the designed water-storage level. But the geologic structure at the central part of the reservoir is quite complicated and karst is quite developed, and there is cave and fault collapse-body on the left bank near the entrance of the underground river, which easily leads to leakage around the dam. According to the engineering geological conditions at the central part, the 0+085 dam site is arranged in the D3g impermeable layer, where the impact of caves can be kept away and is good for construction for the site being close to the river’s entrance. Furthermore, seepage-proof engineering is conducted to the leakage passages formed by the collapse bodies and the karst fissures with the upper and lower half-closed hanging style curtain grouting. Years of practice shows that the seepage-proof engineering is feasible, the seepage-proof lines and grouting design of the dam site is reasonable, and the cost of the reservoir is low. The seepage-roof engineering effectively solved the county water supply and irrigation water for 22600 mu of farmland 215000 mu of tropical crop downstream.