Abstract: 84 global big and giant known gas fields were analysed for systematic mathematical statistics.Natural gas pools were the products resulted from the dynamic equilibriums of generation, accumulation and separation; the newer the age of peak gas generation for source rocks and the more stable the structural conditions were, the more promising the prospect would be. Eogene was the period of peak gas generation for source rocks of global large gas fields; and humic gas fields were formed in coal-bearing series during the early stage of gas generation. Regions with huge volumes of source rocks, peak gas generation and the structural conditions of rather stable subsidence are favourable to the formation of large gas fields.Tarim, South China Sea, East China Sea, West Taiwan Seas, Ordos, Sichuan and Chuxiong Basins, are all favourable regions for the accumulation and preservation of natural gas for their later peak gas generation and stable structural conditions.