The invention provides a device and a method for intelligently detecting dielectric property of fruits and vegetables in microwave-vacuum drying based on low-field nuclear magnetism and belongs to thetechnical field of intelligent detection on drying quality of fruits and vegetables. The microwave vacuum drying technology is adopted for drying fruits and vegetables; sampling is carried out by stages during drying; samples are subjected to low-field nuclear magnetism analysis; dielectric property of the same samples is determined through a vector network analyzer; acquired dielectric propertydata and nuclear magnetism result parameter of the samples are analyzed, and a regression model for expressing the relation between the dielectric property data and the nuclear magnetism result parameter is built by partial least squares regression method, and dielectric property of unknown samples can be predicted according to the model. According to the device and the method, the low-field nuclear magnetism resonance technology is adopted to solve the problem about special requirements on shape and thickness of materials in the conventional dielectric property detection for fruits and vegetables, nondestructive, convenient and intelligent detection on variation of dielectric property in drying process of fruits and vegetables is achieved, and a powerful basis for regulating and controlling microwave power in intelligent drying is provided.