The invention relates to a seawater desalination method and device of natural vacuum and low temperature distillation, which is characterized in that the system must be airtight before operation, the water injection valve on the system top is switched on to fill up the system with seawater; the drain valves of all drainage pipes connected with the evaporation chamber are switched on, then the seawater is flowed out under the influence of the gravity; the air in the system is discharged to make the system vacuum; the heat source can be conveyed to the evaporation chamber now; when the temperature of heat source is higher than the condensation temperature, the evaporation pressure of the heated seawater is higher than the condensation temperature of fresh water, the evaporated vapor is condensed by the condenser under the action of pressure difference between the evaporation pressure and the condensing pressure and finally the desalinated water can be obtained. The invention has the advantages that a sleeve regenerator is arranged on the connection section of the water supply pipe of seawater and the evaporation chamber, the heat of the strong brine discharged by the evaporator is partially adopted to preheat the seawater in the evaporator, the liquid in the system can flow freely due to the pressure difference, thus the method can economize energy source and the device can be used to desalinate the seawater on any sea island, water-deficient area or brackish water area.