EDl equipment belongs to fine treatment water system and usually used in cooperation with reverse osmose (RO) to constitute the ultrapure water treatment system with pretreatment, reverse osmose and EDl devices. EDl equipment replaced the mixed jon-exchange unit used in traditional water treatment technology. EDl equipment requires the electrical resistivity of the water to reach 0.025-0.5 MO.cm and the reverse osmosis device can completely meet the requirements. EDl equipment can produce ultrapure water with the electrical resistivity above 15 MΏ.cm.