This paper presents a systematic study of the constraints of salinity of Quaternary formation water to the growth of micro-fungus, the effect of salinity on solubility of biogenic gas in formation water, and the control of salinity on sealing in the mudstone cover. The Sanhu (three lakes: Taijnar Lake, Suli Lake, Dabsan Lake) area is mainly recharged by Quaternary formation water migrating from south to north, which is supplied by the snow water from the southern Kunlun Mountains, with the highest salinity at the north slope. The fungus growth was restricted by the high salinity of the drainage - collection area at the north slope, therefore a large amount of biogenic gas was generated and separated from the water, while there are better low salinity environments for biogenic gas to form in the central depression and the southern slope of it. The solubility of biogenic gas in formation water decreases with increasing salinity. The low-salinity formation water containing high solubility of biogenic gas migrated from south to north, and then the biogenic gas was separated from the high-salinity Quaternary formation water at the north slope and accumulated there. Experiments have demonstrated that the Quaternary mudstone breakthrough pressure increases by about 100 times when the mudstone is saturated with high-salinity formation water, which means the mudstone sealing ability is greatly improved so that it can effectively seal the free-state biogenic gas. The above studies demonstrate that the biogenic gas generally migrated laterally to the north slope in the form of solution gas, which also suggests that the north slope is rich in biogenic gas resources, and so has a good prospect for gas. Combining the formation characteristics of biogenic gas and the hydrogeological conditions of the Sanhu area, the authors think that the biogenic gas, dominated by solution gas, migrated laterally far away to the north slope in the Quaternary formation water, and then vertically migrated and accumulated in the free state at the north slope.