In this paper, we evaluate the performance of spectral amplitude code division multiplexing (SAC-OCDMA) system in free space optics (FSO) transmission system under various rainy weather (light rain (LR), medium rain (MR) and heavy rain (HR)). Enhanced double weight codes (EDW) are used as signature codes with SAC-OCDMA system. Three users, each carries 10 Gbps, are used with the system. Effects of different propagation ranges and different beam divergence angles are considered in this study. Additionally, the performance of the system is conducted in terms of bit error rate (BER), Q-factor, eye diagrams and received power. Simulation results show successful transmission of $3\times 10$ Gbps with propagation ranges 1.73 km under LR, 1.343 km under MR, and 0.863 km under HF with BER ~ −9, Q-factor ~ 6, and received power −17 dBm.