The dynamics of the replacement of CH4 in hydrate in porous sediments with liquid CO2 was investigated using a self-developed experimental apparatus at different temperatures and initial pressures. The pressure increases steadily as the replacement reaction processes. The amount of the replaced CH4 is almost the same as that of the CO2 forming hydrate in the early stage and gradually becomes somewhat less in the later stage. The initial pressure has minor effects on the replacement rate, and temperature reduction causes a lower replacement rate. The experimental results suggest that the replacement rate is not related to the region of the temperature-pressure conditions but is mainly affected by the fugacity differences of CH4 hydrate decomposition and CO2 hydrate formation.