For studying the actual action area of shock wave in laser shock processing(LSP), the Al2O3 ceramic materials have been impacted at new absorbing layer. The effect of horizontal inflation on actual shock processing is analyzed with the variety of ablation characteristic. The change of transforming area and depth is analyzed through the shock processing of 0Cr18Ni9 austenitic stainless steel and 3A21 antirust aluminum alloy, and the universality of the inflation effect is validated for different materials. It can be found that the inflation of plasma have direct contact with the material of confinement layer.The active function diameter of the shock wave is about 12 mm if the flexible coating is used with the light beam diameter of 8 mm.