In this article, dynamic packing injection molding (DPIM) technology was used to prepare injection samples of Polypropylene-Calcium Carbonate (PP/CaCO3) nanocomposites. Through DPIM, the mechanical properties of PP/nano-CaCO3 samples were improved significantly. Compared with conventional injection molding (CIM), the enhancement of the tensile strength and impact strength of the samples molded by DPIM was 39 and 144%, respectively. In addition, the tensile strength and impact strength of the PP/nano-CaCO3 composites molded by DPIM increase by 21 and 514%, respectively compared with those of pure PP through CIM. According to the SEM, WAXD, DSC measurement, it could be found that a much better dispersion of nano-CaCO3 in samples was achieved by DPIM. Moreover, ?crystal is found in the shear layer of the DPIM samples. The crystallinity of PP matrix in DPIM sample increases by 22.76% compared with that of conventional sample. The improvement of mechanical properties of PP/nano-CaCO3 composites prepared by DPIM attributes to the even distribution of nano-CaCO3 particles and the morphology change of PP matrix under the influence of dynamic shear stress. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012