Abstract: Phthalonitrile resin is a new type of high performance thermosetting resin with excellent mechanical properties and high temperature resistance. In this paper, thermal plastic polyimide (PI) particles were used to improve the mechanical properties of the composites. It shows that the glass transition temperature of the composite decreases with the addition of PI. The introduction of PI can significantly improve the toughness of the composite. The interlaminar shear strength of the composite modified by 10wt% PI is increased by 41.2%, and the mode I interlaminar fracture toughness of the composite modified by 15wt% PI is increased by 156.3%. The presence of particles can be clearly observed between layers of composites. When the mass fraction of PI is further increased, particles will agglomerate, leading to the decrease of interlaminar shear strength of composite materials. In addition, the shear strength of PI toughened phthalic resin composite at 380℃ is similar to that of the unmodified composite, and the PI particle content at this temperature is no longer the main factor affecting the toughness of composites.