Abstract: The temperature of drilling fluid varies greatly when drilling an ultra deep well in deepwater sea area, so the accurate prediction of temperature profile is crucial to the safe drilling of deepwater ultra deep well. In order to accurately predict the borehole temperature profile of deepwater ultra deep well and provide the reference for the drilling design of deepwater ultra deep well, a model for calculating the borehole temperature profile was established according to the principle of energy conservation. In view that the heat transfer mode is different in different hole sections, the hole structure was divided into seawater section, casing section and open hole section for analysis and it was solved by means of numerical method. In addition, the factors influencing the temperature profile was calculated and analyzed by virtue of case calculation. It is shown that the temperature profile of drilling fluid tends to be stable after it is circulated for 300 min. In the whole circulation process of drilling fluid, the temperature difference is up to 150 ℃. The displacement has less influence on borehole temperature and greater influence on the drilling fluid temperature at the bottom hole. And besides, the greater the displacement is, the higher the bottom hole temperature is. The target layer is deeper, so the influence of the inlet temperature on the bottom hole pressure is less. The research results can provide the reference for the safe drilling of deepwater ultra deep wells in China.