A three-stage composite treatment approach of extending preservation period of sea vegetable relates to the preservation and storage technology field of fruit and vegetable. In the invention, firstly,conventional sorting is carried out on the picked fresh sea vegetable, the temperature of the vegetable is decreased via water controlling and vacuum rapid cooling; secondly, the vegetable is treatedby the exogenous nitric oxide with certain concentration; thirdly, modified atmosphere packaging is carried out on the treated sea vegetable via a silicon rubber window packaging container inlayed with silicon rubber membrane. The invention has the advantages that due to combining the advantages of various preservation measures and utilizing the three-stage composite treatment approach accordingto the physiological and biochemical changes of sea vegetable after being picked, the quality change of the picked sea vegetable is reduced to the minimum level, thereby maximum delaying ripening andsenescence process after being picked and obtaining the preservation period as long as possible.