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The benefits of large reserves, wide distribution, and high combustion energy density of natural gas hydrates are of great practical importance to alleviate the energy tension, enhance the existing energy system in China and reduce the greenhouse effect. The CO 2 replacement method is a critical way to develop natural gas hydrate, while traditional experimental methods are difficult to reveal the microscopic mechanism of the replacement system. An MD (molecular dynamics) technique was utilized in this work to simulate the process of carbon dioxide replacement of gas hydrates. This simulation investigates the effects of temperature, pressure, and CO 2 purity during the CO 2 replacement process. CO 2 , different concentrations of CO 2 /H 2 O, and CO 2 /NH 3 are used as the injected fluid. The simulation results show that the influence of temperature on the CO 2 replacement of natural gas hydrate is more significant than that of pressure. Within the temperature and pressure range specified in the simulation, H 2 O inhibits the replacement of CO 2 , owing to the inhibitory effect increasing as the concentration of H 2 O increases; NH 3 promotes the process of CO 2 replacement under the temperature conditions of 250 K and 260 K, and the promotion effect becomes more significant as the concentration of NH 3 increases. However, adding NH 3 inhibits the CO 2 replacement process with hydrate when the temperature lifts to 270 K. These findings provide new ideas to improve the efficiency of the CO 2 replacement method and provide theoretical insight for the engineering exploitation of hydrates., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)