With the development of the energy industry and the continuous growth of global energy demand, the exploration and development of geothermal resources have become increasingly difficult. Deep and ultra-deep geothermal resources have been identified as a key direction for the development of the new energy industry. As the drilling depth for geothermal wells continues to increase, the thermal and physical properties of the drilling fluid are found to have a more significant impact on the calculation of wellbore temperature and pressure amid changes in temperature and pressure. In A coupled numerical model of transient temperature and pressure in the wellbore during the drilling of geothermal wells was established, and the influence of the density and viscosity of drilling fluid on the calculation of wellbore temperature and pressure with changes in temperature and pressure during the drilling of geothermal wells was studied. It was shown by the calculation results that the viscosity and density of the drilling fluid significantly affected the calculation of wellbore temperature. When the changes in viscosity with temperature are considered, the calculation results of wellbore temperature are found to be 3.1% higher, and when changes in viscosity and density with both temperature and pressure are considered simultaneously, the results are 4.99% higher, compared with the case where changes in viscosity with temperature are not taken into account; To improve the accuracy of calculations, the thermal and physical properties of drilling fluid should be fully considered in calculating the temperature and pressure of geothermal wells.