The utility model relates to a ring blowout preventer used for a well drilling, relating to a control device used for a petroleum well drilling, which belongs to an appurtenance used for the petroleum well drilling. The utility model mainly solves the problems that the sealing of the prior ring blowout preventer is not reliable, and the assembly and the disassembly are not convenient as the parts are changed. The ring blowout preventer consists mainly of a casing, and a piston, as well as a rubber core, a stay barrel, and a dust seal which are arranged in the casing. The utility model is characterized in that a top cover is fixed on the casing through a rest shoe, the rest shoe is arranged in the groove of the casing through jaw chuck screws, a wear plate is arranged between the top cover and the rubber core, the rubber core is arranged above the stay barrel and the piston, the dust seal is arranged between the piston and the casing, a measuring hole is arranged on the top cover. The blowout preventer is used for the petroleum well drilling project.