Abstract: In order to study the changes of intermediate products in the process of biogenic coalbed methane genera- tion,the simulation experiments were carried out with 10 kg coal from Sihe coal mine in Qinshui Basin as the sub- strates,and 40 L CBM well water in the same mining area as the bacteria source. The intermediate products in fermen- tation broth were analyzed using GC-MS. The relationship between the intermediates production and gas production was investigated preliminarily. The results show that there were mainly two periods of gas generation. The conversion of aro- matic ring,heterocyclic compounds and benzene derivatives in the substrate into the VFA was found in the first gas generation period. While the high concentration of long-chain alkanes were found in both periods of gas generation.With the sodium acetate,sodium propionate,sodium butyrate,hexanoic acid as the substrate,the same CBM well water as the bacteria source,the process of biogenic methane generation was also investigated. It was found that the acetate, propionate,and butyrate could be converted into methane,while hexanoic acid would inhibit the gas generation perhaps due to its toxicity. The conversions of different organic acids to methane indicated that there were perhaps parity differ- ences in the carbon number of the organic acids. The results above indicate that VFA and long-chain alkanes play im- portant roles in biogenic coalbed methane generation. The production and transformation of VFA and long-chain al- kanes and their influences on the biogenic coalbed methane generation need to be further studied.