Abstract: In this paper, the modulation of light field by the subsurface defects is investigated in detail by solving Maxwell equations employing the finite-difference time-domain method. Meanwhile, the model of three-dimensional defect is set up. Taking cuboid defect as an example, the three-dimensional electromagnetic intensity distribution around the defect is simulated. The maximum electronic field intensity of different defect three dimensional numerical simulation is given. The results show modulation of three-dimensional defect to light intensity is more distinct than that of two-dimensional defect.