The invention discloses a sea 
water desalination device based on pressure retardation 
osmosis and 
reverse osmosis and a method thereof. The sea 
water desalination device comprises a concentration difference 
power unit, a sea 
water desalination unit and a pressure transfer element positioned between the concentration difference 
power unit and the sea water 
desalination unit. The concentration difference 
power unit comprises a hollow seal water chamber No. 1, a hollow concentrated 
seawater chamber adjacent to the hollow seal water chamber No. 1, and an osmotic membrane positioned between the hollow seal water chamber No. 1 and the hollow concentrated 
seawater chamber, and the concentration difference power unit is used for converting 
salinity gradient power of sea water with different concentrations into static pressure. The sea water 
desalination unit comprises a hollow seal water chamber No. 2, a hollow 
fresh water chamber adjacent to the hollow seal water chamber No. 2, and a 
reverse osmosis membrane positioned between the hollow seal water chamber No. 2 and the hollow 
fresh water chamber, and under the effect of static pressure, the 
reverse osmosis membrane only allows water molecules to pass through, thereby achieving sea water 
desalination. The pressure transfer element can move or deform, and transfers static pressure to the seal water chamber No.2 through self moving or deforming. The device has a compact structure, only uses 
seawater salinity gradient energy for sea water desalination, does not consume high-grade energy and is green and environmental-friendly.