Abstract: Offshore oil exploration has been going to marine deep water gradually to find new oil resource in latest years.However,the deep water challenges greatly to well drilling and completion.Nowadays,domestic study of deep water drilling fluid is in an early stage and experiment means is lacking.The method of preventing gas hydrate formation was developed through the close formation study of gas hydrate in deep water drilling fluid system combined with related simulated test results.That is to control the pressure in well-bore by adjusting the drilling fluid in-situ and decrease the water point as low as possible.These experiments and analyses provide useful references to development of marine deep water drilling fluid.