Abstract: This paper optimized the hyperhaline/cationic polymer drilling fluid for deepwater drilling by a lot of experiments. This system is formulated with 20% NaCl as hydrate inhibitors, high molecular weight polymer as flocculant, low molecular weight polymer as clay inhibitor, fluid loss control agent, viscosifier, lubricant, and so on. The lab test results show that it performs good rheology capability, high antipollution capability, high inhibition and good reservoir protection capability. Meanwhile, it can inhibit the gas-hy-drate formation for deepwater drilling at low temperature effectively, and it will reduce the risks of deepwa-ter drilling.