The invention provides a method capable of carrying out high-precision imaging on an internal structure of a natural gas hydrate sediment triaxial mechanical test. The method is characterized in thatthe distinction degree of natural gas hydrate, natural gas and water molecules is enhanced, the imaging resolution of the internal structure of natural gas hydrate sediment is improved and high-precision imaging of the structure in the natural gas hydrate triaxial mechanical test process is achieved by reducing the energy of neutron beams and improving the mass attenuation coefficient of neutron beams based on the fact that the molecular structure size of hydrate is close to the wavelength of cold neutrons. By means of the method, the creep and relaxation rules in the natural gas hydrate sample forming and decomposing process can be obtained, and the dynamic response process of reservoir stability after natural gas hydrate development can be known easily. The method is characterized in that the distinction degree of natural gas hydrate, natural gas and water molecules is enhanced, the imaging resolution is improved and high-precision imaging of the natural gas hydrate dynamic gatheringand dispersing process is realized by reducing the energy of neutron beams and improving the mass attenuation coefficient of neutron beams based on the fact that the molecular structure size of hydrate is close to the wavelength of cold neutrons.