Method for preparing methane from carbon dioxide by using offshore wind power

The invention discloses a method for preparing methane from carbon dioxide by using offshore wind power. The method comprises the following steps: 1) concentrating and separating the carbon dioxide-rich natural gas exploited by an offshore platform in deep and far sea into a material flow rich in methane and a material flow rich in carbon dioxide; 2) carrying out desulfurization and denitrification on the material flow rich in carbon dioxide, exchanging heat with process gas of a methanation unit, and then mixing with superheated steam which is a byproduct of the methanation unit; (3) mixing the carbon dioxide and superheated steam which is a byproduct of the methanation unit, exchanging heat with outlet gas of the high-temperature fuel cell, electrically heating, feeding into a co-electrolysis unit of the high-temperature fuel cell, and electrolyzing to obtain a mixture of hydrogen and carbon monoxide; and 4) performing heat exchange and pressurization on the mixture and the raw material gas at the inlet of