Addition of elastomer to PP can greatly improve its impact resistance,but at the cost of decrease in properties like stiffness and heat resistance．Introduction of inorganic particles into PP can lead to faidy high stiffness,but at the cost of lower fracture toughness．Therefore,to improve the overall performance of PP,a ternary blending method of PP with both rigid inorganic particles and soft elastomefic inclusions has attracted much attention because of its potentiality in achieving both high stiffness and high toushness．A new ternary nanocomposite of PP/styrene-butadiene rubber/nano-CaCO3 was prepared by melt-blending,and its properties and crystallization behavior were investigated．TEM photographs show that the nanocomposite has a“sea-island”microstructure with a“salami” like structure in the dispersion phase,where the nano-CaCO3 particles are embedded in styrene-butadiene rubber particles,This unique phase structure gives the PP nanocomposite excellent pmperties in impacl resislance,stiffness, heat resistance and crystallization rate. Also studied were the effect of the introduction of sodium benzoate and the content of nano-CaCO3 on the ternary PP nanocomposite’s phase structure．crystal form and crystallization kinetics and the effect of the particle size of dispersion phase and the content of βcrystal on the nanocomposite’s properties．It was found that increase of the content of nano-CaCO3 particles and introduction of sodium benzoate into PP ternary system lead to a decrease of the dispersion phase particle size within PP matrix and a great increase of crystallization rate,and consequently result in the remarkable improvement of impact resistance,stiffness and heat resistance of the PP composite．