The invention relates to a method for preparing a substrate-free TiO2 nanotube/nanowire composite array transparent film through synchronous crystallization. The method comprises the following special steps: a) placing a pure titanium foil with the thickness of 0.2-0.3mm in acetone, and carrying out ultrasonic cleaning for 25-40 minutes; then placing the titanium foil in a polishing solution containing 25-40ml/L concentrated sulfuric acid, 15-40ml/L hydrofluoric acid and 60-100ml glacial acetic acid; using 9-11v constant direct current to perform electrochemical polishing for 10-20 minutes; and b) reacting for 5-7 hours under magnetic stirring on the conditions that polyethylene glycol solution with 0.25-0.30wt% of NH4F is used as electrolyte, the titanium foil is used as a positive electrode, a platinum foil is used as a negative electrode, the electrode gap is 3-4cm, the voltage is 60-70V and the temperature is 65-75 DEG C. The method has the advantages that the equipment is simple and the energy consumption is low, thereby being suitable for large-scale production; and the prepared film has no substrate, is transparent and is more suitable to be used as the material of solar cells, supercapacitors and the like.