Abstract: During the drilling and completion in high-temperature and high-pressure deep wells, there are differences between the measured drilling fluid density on the ground and actual drilling fluid density in wellbore because the drilling fluid is affected by both temperature and pressure, which will lead to the difficulties in accurate calculation of the drilling fluid pressure in the wellbore. Based on the investigation on the prediction models of oil-base drilling fluid density at home and abroad, it is considered that all the previous models are not general and the calculation accuracy can’t meet the demands of deep wells, especially ultra-deep wells because they are empirical models using a few experimental data under the condition of specific formulas. Therefore, the paper uses a mathematical analytical method to establish a precise model to predict drilling fluid density and drilling fluid column pressure. Compared with the empirical models of many scholars, it is concluded that most empirical models are the simplified forms of the newly-established analytical model which can reflect the influences of temperature and pressure on drilling fluid density more fully and accurately. In the actual application, regarding the oil-based drilling fluid as the mixture of base oil, salt water and solid material, the prediction for oil-based drilling fluid density and wellbore liquid column pressure with different formula and oil-water ratio can be performed