Abstract: Predicting the aerodynamic and thermal distributions of the plume in vacuum chamber is one of the key prerequisites for developing a large-scale vacuum plume test scheme and improving the simulation effectiveness of the experimental environment. For the ignition test of China's Chang’e-7 leaper, a slip flow computational fluid dynamics (CFD) method taking the adsorption of H₂O and CO₂ into consideration was used to simulate the initial changes in the spatial-temporal distributions of pressure, temperature and gas composition of the plume flow field in a vacuum chamber. The results indicate that both the temperature and mass fraction of H₂O component in the flow field increase rapidly and then decrease smoothly, while the pressure fluctuates upward over time. Based on this conclusion, experimental optimization suggestions are proposed. The method provides a new approach for simulating the plume flow field in vacuum chamber, which may support for the subsequent design of relevant test schemes.