The invention relates to an underground blowout prevention device. The underground blowout prevention device comprises a packer and a circulator, wherein the packer comprises a packer body, a second sliding sleeve and a packing unit are respectively arranged on the inner wall and the outer wall of the packer body, the circulator comprises a circulator body with a circulation hole and a first sliding sleeve arranged in the circulation hole, the second sliding sleeve can actuate the packing unit to pack an annulus, and the first sliding sleeve can open the circulation hole after the packing unit to pack the annulus so as to enable fluid in the annulus to enter a pipe. When pressure of the fluid in the pipe and the annulus, located on the upstream of the packing unit, exceeds pressure of fluid located on the downstream of the packing unit, the first sliding sleeve seals the circulation hole, and the second sliding sleeve continuously moves downwards under action of the fluid, and thereby prompts the packing unit to unseal the annulus. The underground blowout prevention device not only can quickly complete underground packing, but also can pace the large annulus, and thereby reduce danger coefficients of well drilling and well control operations.