NOVELTY - A black zinc oxide is prepared by ultrasonically cleaning zinc metal plate with deionized water and absolute ethanol; adding ionized water; adding sodium chloride, potassium chloride, barium chloride and/or aluminum chloride to the reactor; adding acid or alkali; regulating pH of solution to 3-14; sealing the reactor and heating in thermostatically controlled heating device to react zinc metal plate and to form black zinc oxide on surface of zinc metal plate; cooling the reactor; and washing and naturally drying zinc metal plate to obtain black zinc oxide adhered to zinc metal plate.    USE - The method is for preparation of black zinc oxide for use as photoanode in solar cell and in photolysis of water; as catalyst in photodegradation of organic matter; as photosensitive material in optical sensor; and as template for preparing porous metal, porous metal oxide and porous organic polymer (claimed). The solar cell is particularly a dye-sensitized solar cell, and the black zinc oxide is also used for infrared tracking.    ADVANTAGE - The method has low cost, mild reaction conditions and simple operational steps.    DETAILED DESCRIPTION - Preparation of black zinc oxide comprises:    (A) ultrasonically cleaning zinc metal plate having a 90-100% purity with deionized water and absolute ethanol for more than 20 minutes, and adding ionized water (40-95% the volume of reactor);    (B) adding sodium chloride, potassium chloride, magnesium chloride, ammonium chloride, barium chloride and/or aluminum chloride to the reactor to obtain a solution with deionized water, where chloride ion is present in solution at 0.01-1 mol/L;    (C) adding acid or alkali, regulating pH of solution to 3-14, sealing the reactor and heating in thermostatically controlled heating device to react zinc metal plate at 80-240 degrees C for 1-100 hours and to form black zinc oxide on surface of zinc metal plate; and    (D) cooling the reactor to room temperature, taking out zinc metal plate, washing and naturally drying to obtain black zinc oxide adhered to zinc metal plate.