The invention relates to a device for producing hydrogen and oxygen through photoelectrochemistry composite or coupling, and a method thereof, which belongs to the technical field of green renewable energy. The device is characterized by comprising a solar battery at the upper part and a photoelectrochemistry pool at the lower part; the solar battery at the upper part comprises an electrode base plate, a photo-anode, electrolyte and a counter electrode; the solar battery at the upper part is a silicon solar battery, a dye-sensitized solar battery, an organic solar battery, a chemical compound semi-conductor solar battery or a polymer solar battery and the like; the photoelectrochemistry pool at the lower part comprises a photo-anode, electrolyte and a counter electrode. During use, under the irradiation of sunlight or simulated sunlight, the solar battery at the upper part discharges and generates external bias voltage, and the photo-anode of the photoelectrochemistry pool generates potential or energy. The external bias voltage and the potential or energy generated by the photo-anode of the photoelectrochemistry pool reach the schizolysis energy of water in the photoelectrochemistry pool, and the electrodes respectively generate hydrogen and oxygen. The device is characterized by high conversion efficiency of solar energy and hydrogen energy, low cost, simple process, and easy mass production of hydrogen.