In submerged laser peening, it has been experimentally clarified that the collapse impact of the bubble which occurs after laser ablation is stronger than the impact of laser ablation itself. Moreover, the experimental results showed the arc height increased in proportion to the cube of the bubble development time with various material. Here, the arc height shows the processing capacity of peening, and the bubble development time is proportional to the bubble radius. Therefore, it was shown that the processing capacity of peening by the bubble collapse increased in proportion to the cube of the bubble radius. In order to clarify the effect of bubble radius on submerged laser peening capacity, the fluid/material two-way coupled numerical analysis of a hemispherical bubble on the wall surface with changing the bubble radius was performed. From the analysis results, the relationship between the bubble radius and the maximum pressure in the fluid and maximum equivalent stress in the material was clarified. If the ratio of internal and external pressure of a bubble was the same, the bubble radius had little effect on the bubble collapse pressure and the maximum equivalent stress in the material. However, the material volume of which the maximum equivalent stress exceeded the threshold of yield stress of the materials increased in proportional to the cube of bubble radius. Therefore, also in the numerical analysis, it was shown that the effect of bubble collapse on materials is proportion to the cube of bubble radius.