Abstract: A process for preparing low-dielectric-constant silica film is developed. The dielectric constant of said film are lower than 2.5. Said process comprises a) preparing spin coating solution, said solution being composed of silica precursor, deionized water, alcohol, single proton acid, and polyoxyethylene (20) sorbitan compounds also known as Tween group compounds as templates; the weight ratio of polyoxyethylene (20) sorbitan compounds over TEOS being more than 0.41; b) spin-coating the said solution into a film; c) removing most water and alcohol in said film and making the film react with silicon wafer in soft-bake process; d) removing said polyoxyethylene (20) sorbitan compound of said film in calcination process; and e) Modifying said film to hydrophobic by dehydroxylating said film.