Abstract: Study on the water content, distribution and state change of sea cucumber (Acaudina molpadioidea) by using LF-NMR and MRI had been conducted. Transverse relaxation time T2 of sea cucumber with different rehydration time and thermophilic digestion treatment were measured by LF-NMR. The distribution of free water, extra-cellular water and bound water were observed through T1 weighted image during rehydration processing of sea cucumber. The results showed the content of free water and extra-cellular water increased as the rehydration time growed at the early stage of rehydration and then decreased after thermophilic digestion treatment. The content of free water increased with the growing immersion time while the content of extra-cellular water did not change significantly. LF-NMR provided an effective way to research the physical parameters.