Abstract: During the commissioning of the liquid-phase ethane transportation pipeline, it is necessary to replace the stored nitrogen with ethane and liquefy the gas-phase ethane in the pipeline. However, ethane is easy to be liquefied or gasified at room temperature, leading to gas-liquid phase transition, and thus it is difficult to control the replacement process parameters. Considering the phenomenon of ethane and nitrogen mixing during the displacement, the phase equilibrium characteristics of ethane-nitrogen mixture were analyzed. Hence, the nitrogen replacement process and ethane liquefaction process of liquid-phase ethane transportation pipeline in Lunnan-Korla Pipeline were simulated by LedaFLow software. On this basis, the effects of ambient temperature and flow rate of gas-phase ethane for replacement on liquid holdup, pressure and time of replacement were studied. The results show that whether the gas-liquid phase transition of ethane occurs in the process of replacement is controlled by the flow rate of gas-phase ethane for replacement, while the ambient temperature has little effect. Besides, increasing the inlet flow rate of gas-phase ethane for replacement can reduce the replacement time but increase the mixed gas section. The liquefaction pressure and liquefaction rate are basically not affected by the flow rate of gas-phase ethane for replacement during the process of liquefaction, and the increase of ambient temperature will greatly increase the liquefaction pressure, thus reducing the liquefaction rate. The research results could provide a reference for the formulation of the commissioning plan of ethane transportation pipeline.