Abstract: The technical problems in deepwater drilling such as low temperature,narrow window of safety density,possible hydrate formation by shallow natural gas,and hole slough,etc.,have set high requirement on drilling fluids.A deepwater GTL synthetic-based drilling fluid was developed by studying the amounts of emulsifier and organic clay added,and the water volume fraction effect on low temperature rheological properties and electric stability of the drilling fluid,the formula is 80%GTL and 20%CaCl2 in volume,adding 3%RHJ(compound emulsifier),3% organic clay,3%HiFLO,2%CaO,its low temperature rheological properties,ability to inhibit gas hydrate,and reservoir protection ability for drilling fluid were studied.The results show that the drilling fluid has better low temperature rheological properties,the yield point of the drilling fluid is nearly independent of temperature,it keeps stablity over a wide temperature range;the drilling fluid can effectively inhibit gas hydrate formation under the pressure of 20 MPa CH4 at the temperature of 0℃;and can effectively protect reservoirs,with permeability recovery over 85%,it can meet the requirements of deepwater drilling.