The polarization property of the light beam carrying an image while passing through a multimode step-index optical fiber and its effect on the quality of the image tnransmission by phase conjugation are studied in this paper. The method of filtering the noise is suggested. With this method, main part of the noise can be reduced and the image quality can be improved. Both the theoretiial analysis and esperimentat results are given, and a transmitted image with a resolution of 40 line/mm is obtained.