The accumulation effects in high-reflectivity (HR) HfO2/SiO2 coatings under laser irradiation are investigated. The HR HfO2/SiO2 coatings are prepared by electron beam evaporation at 1 064 nm. The laser-induced damage threshold (LIDT) are measured at 1 064 nm and at a pulse duration of 12 ns, in 1-on-1 and S-on-1 modes. Multi-shot LIDT is lower than single-shot LIDT. The laser-induced and native defects play an important role in the multi-shot mode. A correlative theory model based on critical conduction band electron density is constructed to elucidate the experimental phenomena.