To alleviate the shortage of fresh water resources in the northern China where large-scale brackish water is widely distributed, a multi-stage freezing desalination experiment of brackish water was carried out to reveal the mechanism of water quality changes during freezing out processes. The experiment indicates that the methods of freezing and icing can effectively dilute the brackish water and the desalination rate of ice melt water can reach more than 60%. In the multi-stage processes of salty water freezing, the different freezing rate of various ions can lead to changes of ion composition in ice-melting water at all levels. The conclusion is that the method of multi-stage freezing and desalination of saltwater can be widely promoted and applied in the local for mitigating the predicament of local water shortage and the potential harm of primary salty water irrigation to the environment. The advantages of this desalination are that it can make fully use of natural cold energy in winter and realize well economic and environmental achievements. In addition, it seems to be very simple and practicable, which can be implemented in small-scale households or on a large scale. It is one of the effective ways to solve the difficulties of domestic water use and agricultural water use during the spring drought.