The invention relates to a process method and a device for desalting seawater at low temperature. The process method comprises the following steps that: adding aluminum polychlorid and polyacrylamide into the seawater, and feeding into a multi-media filter; preheating the seawater to 43 DEG C, regulating the pH value to be 4.3, adding acid and feeding into a degassing tower to remove carbon dioxide and dissolved oxygen from the seawater; adding sodium hydroxide, a reducer sodium sulfite and an organosilicon defoaming agent into the seawater, and feeding into a microstrainer to remove small molecular organic matter; adding an organophosphorus corrosion and scale inhibitor into the seawater, feeding into the tube side of a preheater and heating to 72.4 DEG C, and feeding into an evaporator for evaporation; allowing the seawater at an outlet of the evaporator to flow into a first multi-effect evaporation tower to ensure that the seawater is concentrated; and allowing the seawater to flowinto a second multi-effect evaporation tower so as to further finish the concentration of the seawater, obtaining freshwater at an outlet of the sixth-effect shell side of the second multi-effect evaporation tower, condensing by using a condenser, and feeding into a product water tank. Desalted water for boilers can be obtained by the process method, the content of oxygen is less than 3ppb, the content of carbon dioxide is less than 3ppm, and the possibility of dirt growth is also reduced or inhibited in the preheating and evaporation process.