Abstract: During the past time,people thought that commercial coalbed methane gas existed in medium to high coal rank and the low rank coal was not worthy exploring for low gas content.But the cognition has changed now.Some coalbed methane gas fields were found in low coal rank basin such as Powder River Basin in America and Surat Basin in Australia.In these basins,the coal bed thickness is high and gas saturation is also high,thus being favorable to coalbed methane enriching.From the genesis of the coalbed methane in these basins,we can find that most of the coalbed methane was biogenic.In this paper,the authors have carried out coalbed methane enrichment experiment using low coal rank samples from Northwestern China.Experiment results testified that commercial biogenic gas possibly exist in the northwestern coal basins and it was favorable to exploring for high thickness and high resource concentration.