The polyesterification of polyester chip is realized by PTA method and DMT method. PTA is advantageous in low raw material consumption and short reaction period, and has been used as the main process and preferred technical route for polyesterification since 1980s. A large scale production line is a continuous production process, and semi-continuous and intermittent production processes are suitable for medium and small scale production plants. The applicability of PET is not limited by fiber, and has been extended to various containers, packing material, thin membranes, films and engineering plastics.