The invention discloses a method for preparing a super-hydrophobic surface with an ultra-critical CO2 rapid expansion method. The method comprises the following steps of: activating nano-silica with hydrochloric acid, filtering, drying, adding absolute ethanol, adding distilled water, adding two kinds of coupling agents containing fluorine and double bonds, washing a product, filtering and dryingto obtain nano-silica particles containing double bonds; adding the nano-silica particles containing double bonds into an ultra-critical CO2 reaction kettle, stirring, and spraying onto a water-basedpolyurethane paint surface which is end-capped with double bonds and is added with an initiator; and drying, grafting the nano-silica particles onto a polyurethane coating surface to form a stable structure to obtain a super-hydrophobic surface. A process used in the method is environmentally-friendly, the ultra-critical CO2 is a nontoxic, non-flammable and environmentally-friendly solvent, the solvent which quickly expands in a fluid and solute particles are easy to separate rapidly and completely, and no solvent is left in the particles; and the preparation efficiency is high, the method issuitable for large-area preparation, and high film coating stability and high scratch resistance are achieved.