We monitored the gas hydrate through low‐field nuclear magnetic resonance measurement. An observed decrease of the relaxation time (T₂) intensity corresponds to the formation process, whereas an increase of the intensity corresponds to the dissociation process. The right domain of the spectrum with T₂ larger than 10 ms disappears gradually with the formation time, whereas the left domain with T₂ smaller than 1 ms remains invariant, indicating the gas hydrate forms preferentially in larger pores. In addition, the right domain increases rapidly with the dissociation time, revealing that the gas hydrate preferentially decomposes in large pores. The spectrum distributions move toward the fast relaxation domain with the growth of gas hydrate, because the generated gas hydrate occupies the large pore and accelerate the relaxation rate. There is no obvious relationship between the gas hydrate saturation and the porosity, whereas the volume and preliminary dissociation ratio are strongly correlated with the porosity.