A method and apparatus for preparing high-purity water is disclosed. The anionic resin and cationic resin are respectively filled in the electrodialytic fresh water chambers. The fresh water chambers and sewage frames are sequentially arrange to form water purifying unit. When the raw water flows continuously and alternatively through anionic resin and cationic resin, the cations of cationic resin are migrating toward cathode and the anions of anionic resin are migrating toward anode. They come finally into sewage frames. The anions and cations in raw water are adsorbed by said cationic and anionic resins, so purifying the water. |