Abstract: The mechanical properties of reinforced concrete (RC) structures are damaged and degraded after exposure to fire.To investigate the mechanical properties of high temperature-damaged RC slabs strengthened with carbon fiber-reinforced polymer (CFRP), a three-dimensional numerical simulation was carried out based on the "thermal-stress" sequential one-way coupling framework.Firstly, the heat transfer within RC slabs under high temperature was simulated to obtain the temperature field;then, considering the high temperature-degradation of the mechanical properties of steel and concrete materials as well as the nonlinear bond-slip behavior between them, assuming that the interaction between external CRFP sheet and concrete is perfect bond, a three-dimensional finite element analysis model of the high-temperature damaged RC slab strengthened by CFRP was established.On the basis of verifying the rationality of the three-dimensional numerical model, the failure mode, bearing capacity, deflection, stiffness and internal strain of the CFRP-strengthened RC slabs damaged by fire exposures of varying duration were analyzed, and the strengthening effect was evaluated.The influence of the number of CFRP sheets on the strengthening effect was further discussed.The results show that after exposure to fire, the damage pattern of RC slabs subjected to four-point loading is the typical flexural failure.With the increase in fire exposure time, the damage of RC slab is more and more serious while the bearing capacity and the stiffness are reduced.Moreover, the strain of reinforcement and CFRP has increased.With the increase of CFRP layers, the bearing capacity and the stiffness of damaged RC slabs increase, and the strain of reinforcement and CFRP decreases.In addition, when the fire exposure of slabs reaches the fire resistance limit (90 min), the bearing capacity of the slab strengthened with two layers of CFRP can be restored to more than 90% of that in the sound state.