This paper presents a method of the reverse recognition of the check matrix coded by low density parity check code (LDPC), which is based on the posterior probability log likelihood ration (LLR). The posterior probability LLR was obtained by estimating the channel amplification and the variance of the noise in the received code. A reverse recognition of LDPC code check matrix was achieved following the LLR mean value maximization principle. Simulation results show that the receiver can precisely retrieve the LDPC check code used by the sender under different channel circumstances through the LDPC reverse recognition method.