Abstract: Aiming at the Longmenxia-South Coal Mine encountered karst caves in +623m air return adit during construction，6# karst cave is the most complex， uses a combination of dredge and plugging，Using pebble filling and laying drainage pipes to ensure the cave water flow passage, casting the steel rail and reinforced concrete for plugging the caverns, set up the drain pipe in the cavern, install the waterproof gate valve and the pressure gauge,when water pressure overlimit，automatic emission，effectively solving the problem of cavern support and safety.