The invention relates to a method for preparing a BaTi2O5 nano wire. In the method, the nano wire is prepared through molten salt, the selection of a precursor and the control of a technological condition. The method comprises the following steps of: (1) mixing a barium source raw material, a titanium source raw material and a molten salt raw material according to a molar ratio of 1:2:20:20 of BaC2O4.0.5H2O to TiO2 to NaCl to KCl to obtain a mixture; (2) ball milling the obtained mixture in an alcohol or water medium to obtain powder; (3) drying the obtained powder in an oven and then placing the dried powder in a muffle furnace for sintering at high temperature to obtain a product after sintering; and (4) furnacecooling the product after sintering, then washing and drying. The invention has simple process and good repeatability, and the used raw materials are industrial raw materials which have low price and are easy to obtain; during preparing, poisonous metallorganic compounds are not used, thus the method meets the requirement on environment; the nano wire can be prepared in a large scale and is suitable for industrial production; and the application range is wide.