Abstract: Polypropylene (PP) exhibits excellent electrical insulation, chemical resistance and recyclability, possessing broad application prospects in cable insulation. Nevertheless, PP features high stiffness and severe brittleness at low temperatures along with low notched impact strength, and is prone to cracking under long-term service, which limits its engineering application. Blending toughening modification serves as an effective strategy to boost its overall performance.This paper systematically summarizes the molecular structural characteristics and mechanical defects of polypropylene, and mainly reviews the research progress on PP toughening modification with blended systems consisting of rubbers, thermoplastic elastomers, inorganic fillers and nucleating agents. Proper design of blended systems can increase the impact strength and low-temperature toughness of PP while retaining its stiffness and thermal stability. Three core toughening mechanisms are clarified: rubbers and elastomers realize toughening via the craze-shear band mechanism; inorganic particles dissipate fracture energy by means of interfacial debonding and matrix shear yielding; nucleating agents reconstruct the aggregated structure based on melt heterogeneous nucleation.In addition, this work focuses on the synergistic toughening principle of multi-component composite blending. It elaborates the working mechanism that remedies the trade-off dilemma between toughness-stiffness and toughness-dielectric properties existing in single modification, thereby achieving the coordinated enhancement of mechanical and dielectric performances. Future research shall prioritize the optimization of interfacial engineering, the control over the dimension and distribution of toughening phases, as well as the precise regulation of crystal forms and crystallization behaviors, so as to satisfy the demand for synergistically improved mechanical and dielectric properties of insulating materials for high-voltage direct current (HVDC) cables during long-term operation.