Abstract: An introduction was given on various shrinkage process in injection molding，including the shrinkage before gate freezing，that of the part in mold during the cooling stage，and that after dcmoulding. The origin of the shrinkage was sorted to thermal contraction，crystal shrinkage，orientation shrinkage，negative shrinkage，and post shrinkage. The effects on the shrinkage of PP parts were discussed，including molecular characteristics，blending，compounding，and nucleation.The influence of injection parameters，such as including injection temperature，molding pressure，molding time，mold temperature，cooling time，filling speed，and part thickness were also summarized. In the end，the methods of controlling the shrinkage of PP in production process were also referred.

Key words: polypropylene, shrinkage, injection molding, crystallization, orientation