Abstract: For the development of economically desalination technology of whey and improve product quality and additional value. Adopting the whole retentate circle cross-flowing device, desalinization of sweet whey by nanofiltration process was studied in this research. We investigated the variations of salt rejection with or without adding water in the process of nanofiltration, and chosen the appropriate desalting parameters according to the salt rejection index. The results showed that, at 1.1 MPa operating pressure and 4.5 L/min system flow at 30℃, the best effect was obtained under the condition of continuously adding de-ionized water (same as the volume of the retentate)to the rejection liquid with the penetration rate up to 1.5 volume concentration ratio. After spray drying, 45% salt rejection was obtained comparing to the raw whey powder and the whey protein and lactose was completely retained.