Abstract: In order to find out the internal reasons for the difference in biological methane production between weathered coal and lignite, weathered coal and lignite were selected respectively, and the enriched and domesticated bacterial liquid was used as the source of bacteria. The internal mechanism of the difference in biological gas production between weathered coal and lignite was analyzed by biological gas production simulation, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and 16 S rRNA test. The results showed that the biogas production potential of lignite (7.63 mL/g) was higher than that of weathered coal (3.24 mL/g). Compared with weathered coal, in the process of gas production, various groups of lignite fall off obviously, aromatic substances are more converted into other substances with small molecular weight, and phenolic carbon or ether carbon (C—O) oxidation is more obvious, which is conducive to the formation of more small molecular organic acids. Compared with weathered coal, lignite has more serious surface erosion and more pore cracks in the process of biological gas production. The diversity of bacteria and archaea in lignite is lower than that in weathered coal, but the main functional flora accounts for a large proportion. The proportion of Macellibacteroides and Lysinibacillus in bacteria reaches 68.05%, and the proportion of Methanosarcina and Methanobacterium in archaea reaches 89.99%, which is much larger than that of weathered coal. It plays a positive role in the degradation and utilization of organic matter in coal and can provide raw materials for subsequent methanogens. Therefore, lignite is more conducive to the utilization of microbial products to produce methane. Methane metabolism type of weathered coal is methyl nutrition hydrogen nutrition type different from lignite. Microorganisms in lignite can make better use of acetic acid as a carbon source, glucose and glycogen can be effectively degraded into pyruvate, strong oxidation (reduction), and produce ATP for biochemical reactions. The research results provide a theoretical reference for the mechanism of gas production difference between weathered coal and lignite, and provide practical significance for the future biomethanation utilization of weathered coal and lignite.