The invention belongs to the technical field of laser application, and particularly relates to a metal oxide micro-nano structure based on femtosecond laser direct writing as well as preparation and application of the metal oxide micro-nano structure. The preparation method comprises the following steps of: firstly, mixing a metal oxide precursor with a solvent to prepare metal oxide precursor sol-gel, then coating the surface of a substrate with the sol-gel obtain a gel film, and carrying out femtosecond laser direct writing; and enabling the metal oxide precursor to react to generate a metaloxide micro-nano structure by utilizing energy generated by high peak power of femtosecond laser. According to the method, the preparation of the metal oxide micro-nano structure is directly realizedthrough a femtosecond laser direct writing technology, and the metal oxide can be directly sintered without other treatment due to high femtosecond laser peak power, so that the method is convenientand quick. The method is suitable for any hydrophilic or hydrophobic substrate, and can realize the preparation of any metal oxide micro-nano structure with high precision, cross scale and high orientation.