Abstract: Nanosecond laser processing is widely used in the processing of fiber-reinforced composites, but it is easy to produce uncontrollable thermal damage in the laser processing of Kevlar fiber reinforced plastics (KFRP), owing to its poor high temperature resistance. During the nanosecond laser cutting of KFRP, the temperature evolution process was analyzed. According to the ablation threshold theory of laser processing, the ablation threshold and the ablation mechanism were analyzed. Based on the conservation law of energy in heat conduction, the conservation of mass and the conservation of momentum, the damage prediction models of the Kevlar fiber and the resin matrix in the heat-affected zone were established, respectively. The results show that there are significant differences in the heat-affected zone of KFRP laser machining, and the different damage zones can be distinguished by the change law of cutting temperature. The ablation threshold of the Kevlar fiber and that of the epoxy resin matrix are 0.01 J·cm⁻² and 0.005 J·cm⁻², respectively. The theoretical model of the kerf width, the kerf depth and the carbonization zone width is consistent with the experimental result. The heat-affected zone is significantly affected by the laser processing process parameters. Among them, the kerf width is most significantly affected by the laser power, the kerf depth and the width of the carbonization zone are most significantly affected by the scanning speed. But, the heat-affected zone is little affected by the pulse width and the repetition frequency.