Abstract: In deepwater drilling, owing to the impact of deepwater section, the overburden pressure is low, and the density window of drilling fluid is narrow, so that the prediction and control of Equivalent Circulating Density (ECD) becomes more difficult. ECD computational simulation is carried out through hydraulic analysis software for deepwater wells in South China Sea, and the impact of booster pump is analyzed, and the influence laws for ECD in deepwater drilling is discovered, so as to provide the basis for hydraulic parameter design and field operation of deepwater drilling. The research indicates that: in deepwater drilling, it is not only necessary to keep the wellbore clean and control the ECD by adopting the large displacement and controlling the penetration rate, but also necessary to consider the impact by temperature on ECD. In particular, under the circumstance that there is booster pump, ECD will increase gradually as the displacement of booster pump increases.