Abstract: For the rapid repair of various concrete defects commonly found in the spillway of hydroelectric power station, such as cracks, seepage, spalling, and scour pits. A study was conducted for the underwater repair project of the Kainji Hydropower Station spillway in Nigeria. By adjusting the content of epoxy resin and curing agent in the underwater epoxy mortar, different strength grades (C80 and above) of underwater epoxy mortar (concrete) with controllable setting times (initial setting no less than 1 h and final setting no larger than 7 h)could be optimized. The effectiveness in practical engineering applications were discussed, such as angostura teeth and apron slab, and corresponding underwater epoxy rapid repair construction techniques were proposed. The results indicated that the underwater epoxy rapid repair technology had significant advantages in the concrete structures of hydropower overflow facilities. Through material improvements and construction technique optimizations, the operable underwear construction time could be extended by 2 to 4 times without a significant reduction in compressive strength. The technology can effectively enhancing repair effectiveness and structural durability, and ensuring the safe operation of hydropower stations.