Abstract: In order to study the damage mechanism and influencing factors of laser thin films, the principle of radiation measurement based on flat top beam was proposed. The cumulative damage effect of HfO₂ films processed by electron beam thermal evaporation under the repeated frequency laser irradiation was studied by using 1064nm Nd:YAG laser. After theoretical analysis and experimental verification, the characteristics of two measuring methods, 1-on-1 and S-on-1, were analyzed based on the measuring principle of damage threshold. The irradiation laser energy was seeked by dichotomy. Each energy density was irradiated at 20 test points. Zero probability damage threshold and least square method were used to fit and determine the measurement results. The results show that for the same kind of film, the damage threshold measured by 1-on-1 method is 15.75J/cm² and the damage threshold measured by S-on-1 method is 11.90J/cm². The comparison of damage threshold and damage morphology shows that S-on-1 measurement method reflects the typical cumulative effect. The study is of great importance for the study of laser damage mechanism and influencing factors of thin film.