The latest research progress on copolymerization in the field of making high quality of PET flame retardant was stated here, its major content related to the flame retardant mechanisms and fire-resistant properties from five modification methods, namely, the phosphorus copolymerization, the cross-ling of high temperature, the rearrangement of high temperature, the ionic aggregation of high temperature and the end-group capture with chain extension from flame retardant monomers, and their characteristic were also summarized, based on which research directions were proposed.