Retrievable drop-in check valve is an inside blowout control valve.It has a landing sub, which connect the needed position of drill string and put into the well,in order to check valve assembly in place.Retrievable drop-in check valve is a kind of check valve,and it can prevent backflow when well kick,it allows liquid to be injected downward into the circulation well for most of the conventional drilling.Thisvalve can control pressure when drilling and improve,simplify the well control obviously.As long as the check valve is dropped in,it can be in place on the land sub automatically to achieve the purpose of the blowout.In addition,the disassembly of this check valve can save a lot of manpower and material resources compare with the previous drop-in check valve.