The invention discloses a push shot telescopic self-locking device and a push shot telescopic self-locking method for reducing stratum loss caused by a gap of a shield tail. The push shot telescopic self-locking device comprises a concealed box body; an automatic isolation device is arranged at one side of the concealed box body; a push shot device is arranged at the other side of the concealed box body; the concealed box body is provided with an opening for enabling a telescopic self-locking device to enter; the push shot device can reciprocate in the concealed box body, push the telescopic self-locking device to move in the concealed box body and push the telescopic self-locking device out of the concealed box body so as to complete the one-time push action of the push shot device. By synchronously pushing and shooting a telescopic self-locking reinforcement frame in the propelling process of a shield tunneling machine, the push shot telescopic self-locking device takes the effects of filling the gap of the shield tail and temporarily supporting a duct piece and the stratum to avoid generating large stratum deformation, so that stratum loss caused by the gap of the shield tail is fundamentally reduced, synchronous supporting is really implemented when the gap of the shield tail is generated and surface deformation can be controlled better. Moreover, the push shot telescopic self-locking device disclosed by the invention has a simple structure, has high reliability, is convenient to operate and is economic and effective.