Light intensification caused by cracks in fused silica subsurface is one of main factors of laser-induced damage to optical materials. Three-dimensional finite-difference time-domain method is used to simulate parabola-section-model lateral cracks. Moreover, the relationship between light intensification and breadth-to-depth ratioR is discussed. The results show that the morphology change after acid etching is an important cause of damage mitigation. Modulation is very weak and close to each other whenR is greater than 10.0 and it increases rapidly whenR less than 5.0. The electric field intensity reaches a maximal value whenR ranges from 1.0 to 3.0, and the maximal electric field is 4.3 V/m. The electric field intensity of more than 80% samples exceed 2 times than the incident light whenR ranges from 1.0 to 3.5. Intensified area has the skin effect with depth increasing. It is demonstrated that enhanced area lying directly below the crack firstly shifts to left and right sides, then it moves to parabola-section interface and the horizontal interface. Finally, the whole subsurface will be enhanced. In addition, electric field modulation firstly increases and then decreases in the z direction when depth is large enough.