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