Although many approaches [1-3] to calculate overall heat transfer coefficient have been presented, none has addressed the problems associated with (1) irregular and unsmooth interface between cement sheath and formation [4], (2) bad cement quality [5,6] and (3) thermal effect of cement sheath [7] during steam injection. A term "contact thermal resistance" is used to describe the extra heat transfer resistance and added to the overall wellbore heat transfer resistance. This article firstly gives a reasonable method to describe these imperfect contact interfaces. And then a mathematical model for estimating overall heat transfer coefficient and wellbore heat loss is established to analyze the effect of the thermal contact resistance at the interfaces on interface temperature drop, overall heat transfer coefficient, wellbore heat loss and casing temperature. Finally we study the effect of the thermal resistance on steam parameters distribution in the wellbore. The results indicate that the existence of thermal contact resistance produces interface temperature drop, reduces the overall heat transfer coefficient and wellbore heat loss, but leads to the casing overheated. The steam parameters distribution along the wellbore, especially steam quality, differ from the actual values. Moreover, accurate calculation of steam parameters distribution along the wellbore is a good way to save coal resources. (C) 2016 Elsevier Ltd. All rights reserved.