ABS/CaCO3 nanocomposite with super toughness was processed by pressure induced flow (PIF) moulding. After PIF processing, the impact toughness of ABS/CaCO3 nanocomposite improved remarkably, the average highest Izod impact strength of nanocomposite increased to around 69 kJ/m2, which was 2.3 times higher than that of orignal ABS. Moreover, the relative toughening mechanism was investigated. The disk-like rubber domain and the cavities caused by calcium carbonate were researched by small angle X-ray scattering (SAXS). The synergy of them could prevent the craze becoming a large crack effectively.