In deep water drilling, there are challenges to work out the temperature and pressure variation patterns in wellbore and it is difficult to determine the gas influx (overflow) and drilling fluid loss positions, especially under the complex coexistence of overflow and loss conditions. In this study, a transient wellbore temperature and pressure model under the coexistence of overflow and circulation loss conditions was established, based on heat transfer analysis and accounting for the impact of variable mass flow in wellbore annulus on temperature and pressure changes. The analysis of the gas influx and circulation loss coexistence was conducted by defining and calculating the temperature and pressure differences along the annulus. The simulation results indicate that the temperature difference is generally greater under the condition of upper gas influx and lower circulation loss positions compared to that with upper circulation loss and lower gas influx, while the pressure difference is generally greater under the condition of upper circulation loss and lower gas influx compared to upper gas influx and lower circulation loss. An abrupt change of annular temperature difference in an open hole section mostly corresponds to a gas influx position, while a transition in annular temperature difference in an open hole section corresponds to a circulation loss position. A larger initial gas invasion pressure difference can result in a greater annular temperature difference at the wellhead. As the initial circulation loss pressure difference increases, the annular temperature difference at the wellhead decreases.