Abstract: According to different importance degrees,CT images can be distributed into LL₂,LH₂,HL₂ and HH₂by GHM multi-wavelet.The edges of LL₂(with the highest important degree) and HH₂(with the lowest important degree) are detected by strong Canny method.With many thin edges,which are useless for medical diagnosis,patients'information can be hid by deletion and comparison processing of invalid edges.Edges of medical images are modified in order to embed patients'information,so the privacy can be protected under the normal visualization and the existing diagnosis information of patients can be carried safely.