Abstract: Based on the interfacial mass transfer theory of slip-rising bubbles and the gas-liquid two-phase flow theory, in combination with the heat transfer mechanism between wellbore fluid and formation, the paper establishes a fully transient and non-isothermal gas-liquid two-phase flow model considering the interphase mass transfer in oil-based drilling fluid, and the model is verified by O’Bryan’s gas kick experiment data. The research results show that the interphase mass transfer rate between formation gas and oil-based drilling fluid is relatively slow, so that the gas will not be completely dissolved in the unsaturated oil-based drilling fluid immediately, and will be gradually dissolved as the oil-based drilling fluid flows upward along the wellbore. At the same gas kick rate, the volume fraction of the free gas in the wellbore calculated by the above model is slightly larger than that of the previous gas-liquid two-phase flow model considering stable interphase mass transfer. Moreover, the gas-fluid interphase mass transfer rate is increased with the increasing of gas concentration and fluid flow rate. In addition, this model breaks the shortcomings of the previous wellbore multiphase flow model based on stable interphase mass transfer, which can more accurately describe the law of gas-fluid phase flow in oil-based drilling fluid.