The invention relates to a method for preparing anatase-shaped nano TiO2 by combining a sol-gel method and a second hydrolysis method, comprising the following steps: adopting tetrabutyl titanate as a precursor of TiO2, adopting alcohol as an organic solvent and adjusting the pH value between 4 and 7 by inorganic acid; then dropwise adding distilled water and continuously stirring to obtain transparent sol; ageing, drying and then obtaining a loose solid particle; adding distilled water into the prepared gel solid particle; after carrying out ultrasonic wave oscillation, standing and filtering to obtain white powder; and roasting to prepare nano TiO2 powder. An SEM scanned image displays that all powder crystal grains are in a branch-shaped structure, and a TEM image and a grain size analyzer test display that the crystal grain size of the TiO2 is in a nano level. The method has simple process, safe operation, less environmental pollutant discharge, small crystal grain size of a product, difficult conglobation and stable quality and is suitable for large-scale production.