Damages on or near polished substates can be easily observed by TIRM(Total Internal Reflection Microscopy). In our experiments we found that there was a strong dependence of scratch visibility on the angle(φ) between scratches and normal direction of the incident plane. In this paper, the scattered field distribution of a scratch and the imaging properties of a microscope are analyzed. We believe that it is the anisotropy of illumination in TIR-illumination mode that causes the visibility changes of a scratch. After taking this directionality into consideration, we propose an experimental method for TIRM to take picutures with all scratches in all directions in one image.