Underground karst caves are often encountered in tunnel construction of water conservancy projects，especially in Yunnan，Guizhou and Sichuan karst geomorphological regions.The water conveyance tunnel of Jiayan water control project crosses many rivers and mountains，such as Baipu river and Xixi river，and the number and scale of karst caves are large in the construction process.Among them，Yujiazhai tunnel is a large karst tunnel with a total length of 144.5m，a width of 52m and a height of 50m，which cuts off the waist of the water conveyance tunnel.Because the design axis of the tunnel can not be adjusted substantially，it brings great difficulties to the construction of the project.According to the actual situation of large-scale karst caves on site，steel arch concrete arch protection construction technology is adopted，and permanent drainage culverts are set at the bottom of the caves，which not only ensures the smooth passage of the caves when water gushing occurs，but also ensures the safe passage of water conveyance tunnels through large-scale karst caves under the protection of arch protection，thus providing valuable treatment experience for the treatment of large-scale underground caves in the future.