Subsurface defects and contaminations will be generated during the grinding and polishing processes of optical components. Combined modulation is one of the important factors for the laser-induced damages of fused silica. In this paper, by using 2D finite-difference time-domain method, the light intensity distribution modulated by both radial crack and contaminant is studied on front/rear surface, respectively. The results show that the light intensity distribution is significantly affected by the aspect ratio of radial crack and the relative position between radial crack and contaminant. The simulations of the combined modulation on rear surface show that larger LIEFs are generated at certain relative positions compared with those in the single modulation of radial crack or contaminant. Meanwhile, with the increase of distance, the LIEFs are wave-like up and down fluctuations, and gradually tend to stable values. When there is no total internal reflection, the LIEF in contaminant on the crack wall rises significantly with increase of distance, the maximum LIEF occurs when the contaminant is near the intersecting line between radial crack and rear surface. The simulation of the combined modulation on front surface show that the variation of LIEFs in global domain are not very prominent.