The invention relates to a method for seawater desalination and particularly relates to a method for seawater desalination utilizing a double-action gas hydrate. The method is characterized by comprising the following steps: 1) preparing a seawater desalination system which comprises a first reaction kettle, a second reaction kettle, a water pipeline system and a gas pipeline system; and 2) desalinating seawater using the gas hydrate, namely, (1) preparing and generating the gas hydrate in the second reaction kettle and decomposing the hydrate in the first reaction kettle, and (2) when the hydrate is generated in the first reaction kettle, decomposing the hydrate in the second reaction kettle, wherein the production principle is identical to that in the step (1). The method has the advantages of simple equipment, low operation and maintenance cost, low energy consumption and broad application prospects.