The present application discloses a construction method for pouring concrete in a karst cave. Concrete streaming is pumped into a hollow passage of a drill stem, then opens the one-way openable sealing cover with a pre-tensioned spring on a reaming drill bit and enters the karst cave to complete pouring of the concrete. When the karst cave is relatively low, low-slump plain concrete mixed with quick-setting agents is injected through a drilling rig and the hollow drill stem to form a concrete pier; when the karst cave is relatively high, the hollow drill stem is sleeved into a thin-walled steel shell, and the thin-walled steel shell is synchronously sunk into the drilled hole while drilling, enters the karst cave and is socketed into a stable rock stratum, then concrete is pumped into the thin-walled steel shell from the bottom of the pile, and finally, a reinforcement cage is inserted to form a cast-in-place pile. Compared with the existing karst cave treatment methods, the construction method according to the present application can greatly reduce the consumption of materials, improve the mechanization of construction, simplify the construction process, shorten the construction period and reduce the engineering cost, and the cast-in-place pile with thin-walled steel shell, formed when the karst cave is relatively high, can further improve the bearing capacity of the foundation.