A simple method for online measurement of drying process of fruits and vegetables was explored. Relative permittivities of an apple sample and a mixed sample composed of air and apple were measured by LCR meter and matching electrode during a hot air drying process. Then, relation equations between permittivity and relative water content, as well as between permittivity and drying rate, were respectively established. It was found that relative permittivities and drying characteristics were significantly correlated, and correlations between the dielectric constant and the drying characteristics of the mixture were stronger than that of only the apple sample. Conclusions indicated that detecting the moisture content of fruits and vegetables could be more readily achieved with measuring mixed samples instead of only the material itself.