A method for preparing a carbon nano tube/polyacrylic acid hydrogel, a product and an application thereof are provided. The method includes: oxidizing a carbon nanotube into a carboxylated carbon nanotube, thereafter performing in-situ polymerization with acrylic acid, sodium hydroxide, ammonium persulfate, triethanolamine and N, N-methylenebisacrylamide to obtain a carbon nanotube/polyacrylic acid hydrogel. The hydrogel has a uniform porous structure, facilitating a rapid transmission and supply of water. The carbon nanotubes in the hydrogel are of an array structure, achieving a full absorption of solar energy to realize a high-efficiency photothermal conversion. The gel is attached to a sponge base to obtain a solar-powered carbon nano tube/polyacrylic acid hydrogel steam generator for the photothermal conversion. The steam generator is used for solar seawater desalination, but can improve evaporation rate and evaporation efficiency. In addition, the steam generator has many advantages, such as energy conservation, environmental protection, simplicity and practicability.