Solvent transport in poly(ethylene terephthalate) (PET) and related phase transformation were investigated. The data of mass sorption were analyzed according to Harmon's model for Case I (Fickian), Case II (swelling), and anomalous transport. This transport process in PET is accompanied by the induced crystallization of the original amorphous state. The transformation was examined by wide-angle X-ray scattering, small-angle X-ray scattering, differential scanning calorimetry, and Fourier transform infrared spectroscopy. During this process, the matrix is under a strain state that causes different kinetic paths of crystallization as compared with that by thermal annealing. This state of strain assists the development of the solvent-induced crystallization. The model regarding crystallization was proposed in terms of the study of long period L, the crystal thickness l(c), and the thickness of amorphous layer l(a), obtained from the one-dimensional correlation function and interface distribution function. Different kinetic paths were discovered for different crystallization processes.