Abstract: The relationship between the phase structure of PSF/epoxy blend system and brittle/ductile transition was investigated, and the toughening mechanism was analyzed by studying the peeling strength of PSF/epoxy system, DMA and SEM fracture morphology. The results show that the blend system demonstrates good toughness when dispersed epoxy particles are covered by the continuous PSF network film homogeneously, and the thickness of the film is less than 0.04μm. Meanwhile the plastic strain produced in the ductile PSF film on fracture makes the system more flexible, and a toughened structure and toughening mechanism are different from that of traditional “sea island” structure. This resulTis of significance to develop resin matrix with excellent toughness of advanced composites and structural adhesives.