The speciality and application of the reverse osmosis and electro-deionization (RO -EDI)desalination system are introduced.The RO -EDI desalination system has some advantages :the quality of the produced water is high;the system runs continuously and automatically without anybody on duty;it is easy to be used;the environment cannot be polluted for not using acid and alkali;the equipment and corresponding workshop are small;and the running expanses are cheap etc.Some problems about the materials (ion exchang membrane and ion exchanger )used in the homemade equipment EDI, and their stuffing and stuffing mode are stated emphatically.