A new strategy for fabricating polypropylene alloy with good low-temperature toughness was reported. Glass transition temperature (T-g) of rubber phase in polypropylene/ethylene-propylene rubber/poly(styrene-b-ethylene/propylene) diblock copolymer (PP/EPR/SEP) blend was continuously reduced through strengthening the interfacial tensile force on rubber phase by using the concept of mismatched thermal expansion coefficient. As a result, the brittle-tough transition (BIT) of PP alloy shifted to lower temperature and subsequently excellent impact strength at low temperature was achieved. Through qualitative analysis of impact force, it was found that the theoretical temperature at which BIT occurred was close to that obtained by experiment, indicating BIT of rubber toughened plastic system is indeed controlled by rubber's T-g at impact instant. Furthermore, the PP alloy with excellent low-temperature toughness shows balanced toughness-rigidity, on the contrary, the blends presents poor rigidity when SEP or EPR is used to toughen PP alone. (C) 2017 Elsevier Ltd. All rights reserved.