In order to study the law of internal water migration in the process of potato chip heat pump drying, the changes of transverse relaxation time T2 and peak area A2x were analyzed by low-field NMR technique, and a dynamic model was established for different states of moisture change in the drying process. The results showed that in the process of heat pump drying, increasing the hot air temperature can significantly increase the drying rate and accelerate the migration rate of bound water, immobilized water and free water. In the drying process, the free and bound water was changed before the immobilized water, and the free water content was remained basically the same for the first 90min, and then dropped rapidly. The proportions of the immobilized and bound water both showed a rise and then decrease. In the trend, after the free water was removed, the immobilized water and the bound water successively reached a maximum value, and as the drying proceeding, the flowing water was gradually removed, and then the bound water started to be removed until the drying was completed. The heat pump drying process of potato slices belonged to internal diffusion control, and the effective water diffusion coefficient was ranged from 5.228×10-8m2/s to 1.434×10-7m2/s. A dynamic model was established for the changes of moisture content and its content in different stages of potato slice drying with time. The coefficient of determination of all models was greater than 0.98, which was a good predictor of the law of moisture migration of potato slices in different states during the drying process.