The invention discloses an integral double-effect plate type seawater desalination device and a working method thereof and belongs to the field of seawater desalination. The integral double-effect plate type seawater desalination device is characterized by being formed by compressing a series of seawater desalination plate sheets, wherein two different sealing strip structures are arranged between two adjacent plate sheets at intervals. Each seawater desalination plate sheet is sequentially provided with a first-effect heat exchange region, a first steam-liquid separation region, a second-effect heat exchange region, a second steam-liquid separation region, a condensation heat exchange region from bottom to top; and each plate sheet is also provided with a first steam-liquid mixture channel, a first pure steam channel, a second steam-liquid mixture channel, a second pure steam channel, a seawater inlet channel, a heat source channel, a cold source channel, a fresh water channel, a brine outlet channel and an inter-effect seawater channel. According to the integral double-effect plate type seawater desalination device, with reasonable arrangement of the sealing strip structures, various function regions required by seawater desalination are formed on the two sides of a same plate sheet, so that the compactness of the double-effect seawater desalination device is greatly improved; and due to less used corrosion resistant metal material, the cost is lower.