In order to clarify the role of low-field nuclear magnetic resonance and imaging techniques in the study of food water migration， and to study the drying characteristics， moisture distribution change pattern and quality changes during the far-infrared assisted heat pump drying of Agaricus bisporus， different heat pump temperatures (45， 55 ℃ and 65 ℃) were used to dry Agaricus bisporus， and the transverse relaxation time during the drying process was measured using low-field NMR technique， and the signal amplitude， peak area， MRI images and changes of microstructure and quality of Agaricus bisporus before and after drying were analyzed. The results showed that with the increase of heat pump temperature， the time to reach the drying end point of Agaricus bisporus was 510， 420 min and 390 min， respectively. The drying rate of Agaricus bisporus increases rapidly at the early stage of drying， and then gradually decreases and tends to level off. Three different relaxation peaks could be seen from the T2 inversion spectrum: T21(3-23 ms)， T22 (25-155 ms) and T23 (155-1 084 ms)， representing three different states of water: Bound water， less mobile water and free water， respectively. During the drying process， the moisture content gradually decreased and the degree of bonding of moisture gradually becomes higher， and at the end of drying， the relaxation peaks corresponding to T23 decreased by about 99.80%， leaving only some of the relaxation peaks corresponding to T21 and T22， indicating that the free water was almost completely removed and only bonded water and a small amount of non-flowable water remained. NMR images showed that the moisture was basically removed after 360 min drying at 65 ℃， while the moisture was basically removed after 390 min drying at 55 ℃ and 450 min drying at 45 ℃. The moisture on the outside of Agaricus bisporus was removed first and the moisture on the inside migrated outward， and the higher the temperature， the faster the internal moisture migration rate. In addition， BI values at 65 ℃ were 30.55% and 22.69% lower than those at 45 ℃ and 55 ℃， respectively， indicating that 65 ℃ could better maintain the original color of Agaricus bisporus. Furthermore， the ascorbic acid， total phenol， and total flavonoid contents of dried Agaricus bisporus at 65 ℃ were 84.61%， 55.80%， and 36.77% lower than before drying， respectively， and the nutrient loss of Agaricus bisporus at 65 ℃ was the smallest compared to those at 45 ℃ and 55 ℃. This study showed that low-field NMR and imaging technology provided a direct reference for the change of water content in the drying process of Agaricus bisporus， and this study could provide a reference for optimizing drying parameters and improving product quality by the far-infrared assisted heat pump drying process of Agaricus bisporus.