With the shifting mechanism of ions under the effect of electric field in water environment, characteristic of cation and anion through selective semi-permeable membrane and the capability of ion exchange resin, EDI can move cations and anions to concentrated cells, so that water can be purified. It can replace normal mixed exchanger. The electrical resistivity of the processed water can reach above 17MΩ/cm. Meanwhile, it does not need to be regenerated through acid and base like MB.