The Charles-model in closed system is discussed in this paper. The Charles-Law isusedto calculate and analyze the formation and dissociation of gas hydrate. Through the experiment, the formation and dissociation process, development, equilibrium conditions and output forecast of methane hydrate of different water contents in porous media were discussed. In the media with temperature difference, the water, against the gravity, moved to the cold part to form the hydrate. In the experiment, the hydrate output was forecasted through the change of Charles-value and the hydrate would form quickly in 240 minutes when the equilibrium conditions were reached. And the water content affected the hydrate output linearly. At the same time, the formation and dissociation process of methane hydrate in low-temperature and high-pressure environment were observed by CT directly. By the CT images, the moisture migration in porous media, density changes, the movement of the media and the density distribution after dissociation could be obtained.