Given the fact that traditional linear block code identification methods cannot be applied to low density parity check (LDPC) codes, an ant colony algorithm is adopted to optimize the dual space search, so as to realize the LDPC code identification. The atmospheric laser communication channel model and the LDPC codes identification model are established, and the logarithmic likelihood ratio function of calibration relationship under the turbulent atmosphere channel is given. Then the basic ant colony algorithm is combined with LDPC code identification, the logarithmic likelihood ratio function is transformed into the objective function, and the recognition of LDPC codes is realized through continuous iteration for optimal value and optimal search path in the process of ants searching. The simulation results show that under the condition of 256 code length and weak turbulence, when the signal-to-noise ratio (SNR) is not less than 8 dB, the recognition rate can reach 78%; under strong turbulence, when the SNR is not less than 10 dB, the recognition rate can reach 77%. In addition, the parameter settings in the ant colony algorithm have a great influence on the algorithm performance and should be chosen according to actual situations.