Abstract: How to enhance the anaerobic biodegradation efficiency of coal and increase the methane production is one of the key problems to be solved urgently for the microbial production of coalbed methane.In order to study the effect of corn straw addition on lignite bio methane production under the action of exogenous bacteria,the co fermentation experiment of straw and lignite was conducted to study the effect of different straw addition on lignite anaerobic degradation gas production.GC-MS,FTIR and molecular biology methods were used to analyze the product difference,residual solid functional group difference and microbial group difference in the fermentation broth at the end of co fermentation and single fermentation.The results showed that when the mass ratio of corn straw to Shengli lignite was greater than 0.45,it promoted the bio methane production.However,when the mass ratio reaches 2.00,the methane output decreases significantly.GC-MS analysis shows that the substances at the end of degradation are mainly fatty acids,fatty acid esters,phenols,aromatic acids,aromatic esters,alcohols,ketones,nitrogenous compounds,etc.At the end of reaction, there are few substances in the fermentation broth of straw/coal co fermentation system, and there are many kinds of substances accumulated in the late stage of single straw and coal gas production,indicating that the intermediate products degraded in the co fermentation system are utilized.FTIR analysis showed that the residual straw and coal at the end of the reaction were absorbed in aromatic,oxygen containing,fat and hydroxyl functional groups,while the co fermentation residues were not absorbed,indicating that the co fermentation substrate was completely degraded.Molecular biological analysis showed that the main bacteria in co fermentation and single fermentation systems were S50_ wastewater-sludge_ Group, W27, Desulfovibrio,etc.The addition of straw led to the decrease of the number of sulfate reducing bacteria in the co fermentation system, and the increase of the number of some fermentation bacteria. Methanogenic bacteria in H₂/CO₂ reduction pathway are mainly involved in straw fermentation to produce gas,while methanogens in acetic acid pathway are involved in lignite fermentation to produce gas.The addition of straw makes the methanogenic pathways diversified,thus promoting the biodegradation of coal to produce gas.