In order to prevent working environment pollution, a blowout preventer is necessary to carry high-speed upward downhole dust or slurry away from the hole top during DTH hammer drilling. Comprehensively considering the main factors of the structure characteristics of hole top workbench for truck driller, the shape features of matched drill pipe with taper at the joint, the drilling process characteristics and the mount-dismount operating conditions, a low pressure blowout preventer for air DTH hammer drilling used on top drive truck driller was designed with the advantages of simple structure and convenient installation. The borehole entrance sealing was conducted by interference fit between rubber sealing plug and drilling pipes, the sufficient compensation quantity of rubber sealing plug is effective for sealing of those pipes with large outside diameter difference; the rubber sealing plug can be easily replaced while adding drilling pipes; 2 diversion ports were set up to reduce returned fluid pressure drop. It is showed by the field application that the blowout preventer can effectively prevent the dust or slurry leakage and obviously improve the construction environment.