A two-phase ejector is a device that induces suction flow without using a pump or electricity and can be used as a refrigerant circulation method for turbo refrigerators and car air conditioners, etc. Benefits of passive equipment include maintenance-free, reduced costs, and improved COP. The flow inside the two-phase ejector consists of a driving flow and a suction flow. When the driving flow expands as it blows out from the driving flow nozzle, the thermal energy potential is converted into momentum, which can be applied to the suction flow to induce the flow without using external power such as a pump. Mixing of driving and suction flows with evaporation and condensation at gas-liquid contact surfaces depends on thermal-hydraulic parameters and flow rates, which need to be controlled to maintain the driving force. Those parameters can easily be out of operating range with a slight change in balance. Also, there is little knowledge of heat and mass transfer to find and design operating conditions and ejector configurations, so it is important to obtain knowledge of them by CFD analysis. In this study, a heat and mass transfer model of the gas-liquid interface in a critical two-phase flow has been developed. To deal with the thermally non-equilibrium two-phase flow in which evaporation and condensation occur simultaneously at the gas-liquid interface, we implemented constitutive equations such as the correlation of the interfacial area concentration into the CFD tool, and evaluated the evaporation coefficient, which is an important parameter determining the phase change rate, based on the physical properties of the working fluid. The CFD simulation method is validated using experimental data of a two-phase ejector with a refrigerant. In the validation work, the flow rate of the driving flow and the suction flow and pressure distribution in the ejector were compared to confirm the validity of the developed CFD simulation method. The predictive accuracy of the flow rate ratio (suction/drive) was -33%. We propose a mechanism to change the suction flow rate by changing the tip position of the driving flow nozzle, and plan to examine the performance in actual refrigerant systems using ejectors with different nozzle positions.