Depressurization has been considered an economic and practicable method for natural gas hydrate (NGH) exploitation. To obtain the kinetic data of methane hydrate (MH) dissociation under different backpressures, MH dissociation by depressurization in a porous medium was investigated in situ using magnetic resonance hinging (MM). MH was dissociated under backpressures that were varied from 2.8 to 2.2 MPa, and the hydrate saturation variation during dissociation was analyzed. One experimental case was carried out with constant backpressure, and four cases of variable backpressure depressurization experiments were carried out. The radial dissociation pattern during depressurization was confirmed. During hydrate dissociation, free water was observed to move toward the outlet of the vessel and decreased the water saturation after the hydrate totally dissociated in the field of view (FOV). The MRI data provided excellent information on the spatial distribution of water in the porous media during hydrate dissociation.