Abstract: As a kind of unconventional gas resources with great potential,the gas hydrate has raised great attention from the international society.It is not only an important supplement and substitutes to conventional natural gas resources,but also a kind of green and efficient low-carbon energy.According to the geological conditions for its formation and distribution,we made a comprehensive review on the geological and geochemical characteristics of gas hydrate in a global viewpoint,discussed its genetic type and its relation with source of gases.A summary of the progress of exploration techniques,in particular the progress in China,is also presented.