In order to meet the demand of rapid workover under pressure of coal bed methane(CBM) wells,and solve the problem that the rubber core of the original blowout preventer needs to be changed frequently because of serious wear,a air forced annular blowout preventer was designed.This blowout preventer utilizes the principle of air compression to realize the rapid passage of the tubing collar,its shell and rubber core are connected by the spline to facilitate the replacement of the rubber core.The sealing properties of the key component of rubber core were analyzed by ANSYS,the relationship between the contact pressure and the control pressure was obtained.The damage cause and the failure form of the rubber core were analyzed.The results show that,with the increasing of control pressure,the sealing pressure of the air forced annular blowout preventer is increases gradually,and the sealing pressure stabilizes at around 7 MPa when the control pressure is 4 MPa,which meets the sealing requirements in the workover.The pressure in the upper part of the rubber core is the most intensive and prone to cause overflow phenomenon,the curing of this part should be strengthened.