As free space optical communication(FSO) is affected by the atmospheric turbulence,the channel coding technique is used to ensure the stability of FSO system.The principle of LT code was studied,and LT code was introduced to the FSO system.The required conditions of the LT code distribution were analyzed,the Poisson robust soliton degree distribution(PRSD) was used to reduce the decoding cost of LT codes and reduce the complexity of coding and decoding,and it is applied to FSO system to improve the performance of FSO system.The performances of PRSD and RSD were compared,and the bit error rate of FSO system in different turbulence channels was simulated by MATLAB.The results show that PRSD has a smaller average degree,and can reduce the decoding cost,the encoding and decoding complexity of LT code.The LT code using PRSD can reduce the bit error rate in FSO system,so it improves the stability of FSO system.