Abstract: The model proposed in this paper can predict the distribution of temperature in wellbore exactly during the whole process of blending diluting oil and viscosity reduction, it also can Optimize process, save resources, enhance productivity. This paper divides wellbore temperature field into two parts which are connected to each other according to actual application of the technology, and establishes a calculated model of temperature field correspondingly. The accuracy of temperature calculation is based on the accurate calculation of overall heat transfer coefficient.The process of heat transfer is divided into steady heat transfer and transient heat transfer when calculating the overall heat transfer coefficient. According to the particularity of thick oil flow, taking forced-convection heat transfer into consideration. Convection flow pattern is decided according to the corresponding formulae and then the corresponding forced-convection heat resistance is added to deduce the computing formula of overall heat transfer coefficient. This model was applied to calculate the wellbore temperature in Well A in Tahe oilfield, and the results of calculation and the reality are uniform largely, which shows the accuracy of this model. This paper is of certain directive significance to the construction site of blending diluting oil.