Abstract: To reveal the influence of the heat-insulating coating on the wellbore temperature field of ultra-deep wells, the comprehensive heat transfer coefficient of the drill pipe was calculated in the form of heat transfer resistance according to the thermal conductivity characteristics of the heat-insulating coating and the drill pipe. A transient heat transfer model of the wellbore-formation of the ultra-deep well considering the heat-insulating coating inside the drill pipe was developed. The model was discretized by the finite difference method and solved iteratively by the Gauss-Seidel algorithm. The accuracy of the model was validated through theoretical analysis and field data. The results show that the thermal conductivity coefficient of the heat-insulating coating inside the drill pipe significantly affects the bottom hole circulating temperature. A decrease in conductivity coefficient leads to a rapid drop in wellbore annular temperature and an increase in exit temperature. The thickness and length of the heat-insulating coating also greatly impact wellbore temperature, with greater thickness resulting in a lower bottom hole circulating temperature. These findings offer essential theoretical support for wellbore temperature control and optimization of heat-insulating drill pipe parameters during ultra-deep well drilling.