Abstract: In this paper, the influences of interfacial adhesion and glass fiber content and cooling rate of the specimen melts in injection molding process on the matrix crystal structure and mechanical properties of GF/HDPE composites were investigated by using SEM, SALS, DSC, material universal testing machine, etc. The results show that the produced interfacial stress from the shrinkage of specimen melts in injection molding process can strain induce the forming of the extended chain crystals in the matrix and obviously improves the mechanical properties of the composites.