In order to reduce the influence of turbulence and improve the performance of free space optical communication systems, a system model based on the multiple-beam transmission and reception techniques with 4 transmission antennas and 4 reception antennas and orthogonal space time block code (OSTBC) method is proposed. The method′s average bit error rate performance is studied. The simulation results show that the scheme possesses superiority on diversity and could achieve the largest space diversity gains with diversity degree is 16. It also can realize full transmits speed, which is similar to the traditional Alamouti scheme. The revised decoding algorithm can be applied in multiple-beam transmission and reception systems with 1, 2 or 3 receiving antennas.