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 absorbed and scattered by the atmosphere. As a result, the transmission quality of the OAM beam is seriously degraded, which in turn affects the stability and reliability of the FSOC system. Based on the theoretical knowledge of OAM multiplexing technology and atmospheric turbulence model, this paper analyzes the influence of different turbulence intensities on the bit error rate and channel capacity of OAM beam transmission, and analyzes the multiple-input multiple-output (MIMO) equalization technology. And adaptive optics (Adaptive Optics, AO) technology respectively introduces the mitigation effect of FSOC system on atmospheric turbulence, compares and analyzes the advantages and disadvantages of different algorithms in the two technologies, and summarizes and prospects the technology development status.