Abstract: Wellbore-formation temperature is one of the key factors that affects the wellbore pressure control, the sidewall stability prediction, and the optimization of mud motor and measuring equipments. Based on the energy exchange mechanism of individual control-unit components of wellbore and formation during circulation and circulation-stop periods of drilling fluid, we established a coupling numerical model for wellbore-formation transient heat transfer during circulation and circulation-stop periods under conditions of the actual downhole string assembly and casing program. Combined with basic data of a deep well, we analyzed wellbore and formation temperature distributions during circulation and circulation-stop periods and the results showed that the wellbore temperature distribution is remarkably influenced by casing length and the annular temperature in the casing section hardly changes with increasing the circulation and circulation-stop time. However, the annular temperature in the open-hole section decreases with the increase of the circulation time, while it gradually increases with the increase of the circulation-stop time. The disturbance distance of drilling fluid to the formation temperature is commonly about 2.8m during the circulation process, while it is about 4.6m during the circulation-stop period.