In a LiNbO$_{3}$ crystal, optical noise is caused by the inhomogeneity of crystal inside if the excess energy is incident on the crystal. In this paper, we experiemnt the influence of optical noise when it is applied for beam diffraction and optical information storage. And it is proposed the energy threshold level which is not affected by optical noise in Fe-LiNbO$_{3}$ crystal(0.02Wt.% doped, 10mm*10mm*10mm). The optical noise of crystal weremeasured as a function of the incident beam intensity(10mw, 5mw, 1mw, 0.5mw), direction in incident(orthogonal, left rotation, right rotation) and wavelength(514.5nm, 632.8nm).