Free space optical communication (FSOC) based on orbital angular momentum (OAM) has the advantages of large communication capacity and fast information transmission. The FSOC system uses the atmosphere as the transmission medium, which will be affected by atmospheric absorption and scattering. As a result, the transmission quality of the OAM beam is seriously degraded. Based on the theory of OAM multiplexing technology and atmospheric turbulence model, this paper analyzed the influence of different turbulence intensities on the bit error rate and channel capacity of OAM beam transmission, and analyzed the research status of the mitigation effect on atmospheric turbulence by introducing multiple-input multiple-output equalization technology and adaptive optics technology respectively into FSOC system. The inhibition effects of different algorithms in the two technologies were compared and analyzed, and the technology development status was summarized and prospected.