By combining GC and FTIR characterization, the existing form, content and migration of diethylene glycol (DEG) in PET container for food packaging were investigated. In addition, a fast and accurate external standard method was established to determine the total quantity and monomer quantity of DEG remained in PET container. The results showed that DEG molecules existed in the PET are in the form of interchain aether bonds and monomers, and the previous form dominates. Furthermore, the DEG migration results revealed that the migration quantity is the highest in an acid food simulant under the most severe condition; the migration quantity increases with temperature rising and time extending.