Carbon fibre reinforced polymers (CFRP) are widely used in building reinforcement projects. However, due to the poor high-temperature resistance of epoxy resin adhesive, early peeling between carbon fibre reinforced polymer and concrete occurs, and the composite structure loses more than 60% of its load-bearing capacity, which seriously endangers public safety. A ternary synergistic reinforced flame retardant system consisting of cellulose nanocrystals (CNC) modified polyvinyl alcohol (PVA) fibres and ammonium polyphosphate (APP) was designed. And the addition ratio of APP, PVA and CNC was optimised by three-factor three-level orthogonal experiment. The following conclusions are drawn: ammonium polyphosphate can effectively resist the fire temperature, and effectively control the internal temperature of the colloid at 100 ℃ through the formation of an expanding carbonation layer; PVA fibre filaments can further enhance the toughness of the epoxy resin adhesive, and the toughness can be increased by 30% through the bridging effect of the fibre filaments; the experiment found that the fire-resistant property and the toughness-enhancing properties of their respective indexes are good, and through the synergistic modification of ammonium polyphosphate and PVA fibre filaments, the colloidal layer will not produce Conflict point, which is crucial for the high temperature field in the later stage. The conflict point provides a better reference for the CFRP reinforcement and strengthening project in the high temperature field at a later stage.