[Objective] The composition and diversity of microorganism during low rank coal authigenous microorganism methane conversion were explored in Xinjiang. [Methods] We evaluated the effect of low rank coal authigenous microorganism on methane conversion and organic acid content by anaerobic culture. The dynamic changes of microbial community were analyzed by terminal restriction fragment length polymorphism (T-RFLP) in Hami’s long flame coal. [Results] The results suggested that lang flame coal and brown coal had little influence on methane production of indigenous microorganism. As low rank coal biological methane conversion time went on, methane production showed an increasing tendency. The yield of long flame coal biological methane was 10.28 mL/g and the concentration of volatile fatty acid (VFA) were the lowest at 60 days. The diversity indexes of microbes did not change significantly. The major microbial groups were Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria in different low rank coal conversion period. The bacterial community structure was more complex, while the methanogens community structure was relatively simple. All samples harbored these phyla such as Methanosarcina, Methanohalobium, Methanolobus, Methanomethlovorans, which constituted a basic flora of community structure. [Conclusion] There was abundant microbial diversity in different low rank coal conversion period and the diversity was different in different period. The methanogens community structure was relatively simple, and the number of common groups was higher in methanogens community.