Biogenic gas is the product of methanogen in anaoxic environment.Its formation and occurrence is controlled by the distribution of methanogen.The present method in studying the distribution of methanogen is MPN(numbers of methanogen).Because methanogen is strict with its environment,especially with the occurrence of oxygen,trivial change should disturb the bacterial collects and make the number different from the reality.Otherwise,collection of the fresh groundwater is difficult for us.All those make MPN turn to be hard to be dealed with.The concentration of some special biomarkers of methanogen,especially its core membrane components,could reflect the distribution of methanogen for a time.This method is simple and easy to operate,could make up the deficiency.In this paper,the distribution of archaeol,the core membrane structure components,is analyzed in the sediment from two wells in the Sanhu depression Qaidam basin.The results showed a good relationship between methanogen and salinity.In high salt area,the activity of methanogens was depressed in the shallow(above 1000m),and then turned to active up to 2000m.While in the surrounding area like Sebei 1 area,the salinity of sediment is much lower,the depression of methanogen in the shallow is slight that make methanogen mainly concentrate above 1000m and is low below 1000m.In the final,combined with the sediment palaeoenvironment and salinity of the sediment,the activation of methanogen in Sanhu depression is characterized.