Blowout preventer for wellhead of oil well

The invention belongs to the technical field of well drilling packing equipment, and particularly relates to a blowout preventer used for an oil well mouth, the blowout preventer comprises a shell and a sealing assembly, a through hole is formed in the shell, the two ends of the through hole both penetrate through the shell, the sealing assembly is installed in the shell, and the sealing assembly is used for sealing the through hole; the device further comprises an alternate plugging assembly, the two shells and the two sealing assemblies are symmetrically arranged, the shells and the sealing assemblies are installed in the alternate plugging assembly, and the alternate plugging assembly is used for adjusting the states of the two sealing assemblies. By arranging the alternate plugging assemblies, in the forced tripping process of the drilling tool, one of the two sealing assemblies connected with the drilling tool is in a closed state, and the other sealing assembly is in an open state, so that in the moving