The invention discloses a method for preparing nanometer white carbon black through a gaseous-sol gel process. The method comprises the following steps: taking coal ash as a raw material; roughly extracting, thereby acquiring silicon dioxide; reacting with calcium fluoride and concentrated sulfuric acid, thereby generating SiF4 gas; forming a sol through hydrolysis reaction; adding ethyl alcohol as a dispersing agent in a sol hydrolysis process, thereby effectively preventing the agglomeration of the white carbon black and acquiring the white carbon black with small grain size large specific surface area, high purity, no obvious agglomeration and excellent dispersing property; taking vinyl silane as a modifying agent and adopting the sol gel process for successfully grafting the hydrophobic group vinyl onto the surface of the white carbon black, thereby promoting the hydrophobicity of the white carbon black and the compatibility between the white carbon black grain and the rubber substrate.