During manufacture and in service, various defects might emergence in rails. Some defects are volume ones, and others are planar ones, like facula, greyness, non-welded together and fatigue crack. plane defects are very dangerous. They not only reduce the effective section of rail, but also bring on stress concentration. It is important to detect all the defects to make sure security of transportation. The detection is very difficult owing to complicated shape of CFOSS, large thickness in some places, uncertain positions of defects. The method of detecting the planar defects and the defects located at the rail fillet, for terms of the different parts of a rail, see Fig.4,were mainly discussed in this paper.