The invention discloses a metal oxide as well as a preparation method and application thereof, and the preparation method comprises the following steps: adding salt A and salt B into an alcoholic solution M, stirring until a solid is dissolved, adding an alkali solution into the solution to obtain a mixed solution, enabling the mixed solution to react, and generating a precipitate; uniformly stirring the solution containing the precipitate, carrying out hydrothermal treatment, and reacting to obtain a metal oxide; wherein A is one or more of a positive divalent metal element and a positive trivalent metal element, and B is a positive trivalent metal or a positive tetravalent metal, and is one or more of a positive trivalent metal and a positive tetravalent metal. The perovskite type metaloxide and the preparation method thereof solve the problem that when an electron transport layer is prepared from a perovskite type metal oxide prepared through an existing method, high-temperature annealing is needed, and a QD layer is prone to damage.