Abstract: The interlaminar fracture toughness of carbon fiber reinforced epoxy resin (CF/EP) composites was studied. The type II interlaminar fracture toughness (G_IIC) was studied by adding four kinds of inorganic nano-particles and three kinds of thermoplastic particles into the interlaminar of CF/EP composites . One kind of inorganic nano-particle and one kind of thermoplastic particles with good operability and tougheness effect were selected to study the synergistic toughening property. The results show that the G_IIC of CF/EP composites is improved with appropriate inorganic nano-particle, which is mainly due to the micro-structure formation between layers and fracture energy absorbed effectively. The comprehensive properties of nano sheet boehmite (AlOOH) are the best. When the content of AlOOH nano particles is 1wt%, the G_IIC of CF/EP composites reaches 931 J/m², which increases by 29.3%. Among the thermoplastic particles, the modified poly (aryl ether ketone) (PAEK) has the best comprehensive properties. Adding 10 wt%PAEK in the layers, the G_IIC of the CF/EP composite can be increased by 32%. This is due to the diffusion of thermoplastic particles between layers along with the flow of EP matrix, forming a unique interlaminar continuous structure, which increases the resistance of crack propagation and effectively improves G_IIC of the CF/EP composites. The G_IIC of the CF/EP composites toughened by both 10wt%PAEK and 1wt%AlOOH reaches 1 368 J/m², compared with the non-toughened CF/EP composites , which is increased by 90%. The toughening effect is greater than the sum of adding PAEK and AlOOH. This shows that the addition of both PAEK and AlOOH into the interlayer of CF/EP composites has a synergistic toughening effect.