Optical Interleaver Division Multiple Access(OIDMA) system is a conceptually simple, yet still efficient solution for Free Space Optical(FSO) communications, due to its high bandwidth efficiency and low complexity of Multi User Detection(MUD). The Extrinsic Information Transfer(EXIT) chart is an efficient tool for analyzing iterative structures. By using EXIT charts, the OIDMA FSO system over deep-space and deep Gamma-Gamma atmospheric turbulence fading channels is analyzed. Experimental results show that the OIDMA FSO system exhibits a rapid convergence, as well as excellent system performance in different scenarios. At the same time, EXIT chart is proved to be able to analyze the OIDMA FSO system accurately and effectively, which has important guiding significance.