With the strengthening of exploration and development of deep strata and offshore oil and gas resources, more and more deep wells and deep-water wells have put forward higher requirements for drilling fluid performance. The high-temperature high-pressure of deep well and the low temperature environment of deep well have important influence on the rheology and density of drilling fluid. A new method for calculating the rheology and density of high -temperature high-pressure (HTHP) drilling fluid is proposed and studied in this paper. In this paper, the HTHP rheological data are used to predict the shear stress under different shear rates, and then the wellbore rheological parameters are predicted and analyzed. For the calculation of drilling fluid density, the classical component method static density calculation model established by Hoberock model based on drilling fluid components is analyzed and improved in this paper. The obtained model predicts that the maximum absolute error of drilling fluid density under different temperature and pressure is 0.02 g/cm3, and the absolute error is controlled within 2 %.