In This paper, Diffraction cones are studied in LiNbO3:Fe. These diffracted cones are shown to result from the degenerate four wave mixing among the incident reflected and scattered beams induced by imperfections in the crystals. The angles of the cones are determined by phase matching condition △k = 0, which can be achieved by Ewald sphere construction from diffraction theory, while diffraction cones induced by degenerate four wave mixing of time-resolution are also discussed.