In this paper,a nanofocus X-ray computed tomography(X-CT)imaging system was used to observe the methane gas hydrate behavior in porous media.A series of experiments have been carried out to illustrate the methodology of identifying methane hydrate from the free gas,water and sand.A pressure vessel was designed to form and dissociate methane hydrate in porous media for X-CT observation in situ.Two methods,improving the solution density and adding a hydrate grain as reference in the porous media,are used to improve the resolution of distinguishing hydrate in the system.The results show that the free gas,sand,water and hydrate can be clearly identified.The spatial relationship between hydrate particle and sand keeps changing in the process of hydrate formation,which is unconnected in the early stage and agglutinated in the later stage.The results also show significant migration of gas and water in the voids of sand,which gives an effective way to assess the permeability of sediments.