K9 glass is widely used in of high-power lasers because of its high hardness, good thermal stability, low expansion coefficient and high transmittance. However, the problem of contaminant-induced damage to optical components has become one of the bottlenecks restricting the development of high-power lasers. The in-depth study of the damage mechanism of optical components is important to control the damage formation. In order to investigate the damage mechanism, the spectral detection analysis method is proposed, and the mechanism of Al2O3-induced laser damage in K9 glass is studied by this method. In this method, the EDS spectroscopy techniques were used to investigate the damage morphology and the corresponding changes in the atomic percentages of elements before and after the damage. The physical and ablation chemical changes that occurred during the damage process can be explored. In addition, the ionization process during the damage is diagnosed and discussed combined with LIBS technology. The investigation of the damage principle of optical elements and the real-time monitoring of the safety of optical elements are realized. The results show that during the laser-induced contaminant damage, the morphology of Al2O3 particle changes and micro damage crater also appeared in the K9 glass. In addition, the atomic percentage content of Al2O3 particles changes due to the deformation of the particles, the Na2O contained in the K9 substrate combines with oxygen, causing an increase of the atomic percentage content of O elements, and SiO2 changes into ultrafine particles through the vaporization-condensation process, which leads to a decrease in the atomic percentage of Si elements. These changes directly reflect the high-temperature melting phenomenon during the damage process. The ionization breakdown process can be detected using LIBS, and the characteristics of a plasma flash in the damage process are obtained. Furthermore, the physical processesmentioned above were modeled and simulated, and the heat conduction during the damage process and the plasma shock wave propagation characteristics within the substrate were analyzed using COMSOL simulations. It is shown that during the damage process, the particle temperature reaches 2 800 K, which is higher than its melting point (2 313 K) and similarly, the substrate temperature (2 500 K) is also higher than its melting point (1 673 K), which directly causes a phase transition and generates a plasma under subsequent laser irradiation. The high-pressure impact of the plasma causes the appearance of micro melt damage craters on the substrate. The simulation analysis verifies the feasibility and accuracy of the LIBS technology and EDS spectral analysis to investigate the damage mechanism of optical components, which can be used not only for the analysis of the damage mechanism but also for the real-time monitoring of the stable operation of high-power laser systems.