NOVELTY - System comprises an electrolysis unit and a photothermal unit. The electrolysis unit comprises a photoelectric unit, a cathode, an anode, an electrolytic tank and an electrolyte. The photoelectric unit is used for converting solar energy into electric energy, and providing required electrolysis voltage or current. The photothermal unit is used for converting the solar energy into heat energy, heating solid electrolyte to reach the molten state, and heating the electrolytic tank to the electrolysis temperature.    USE - The system is useful for driving high-temperature electrolysis of carbon dioxide/water to prepare a synthesis gas by employing solar energy (claimed).    ADVANTAGE - The system is clean and safe; ensures comprehensive utilization of solar resources; achieves electrolytic conversion at low electrolysis voltage and relatively low temperature; achieves utilization of carbon dioxide resources; and is energy saving and environmentally friendly.    DETAILED DESCRIPTION - System comprises an electrolysis unit and a photothermal unit. The electrolysis unit comprises a photoelectric unit, a cathode, an anode, an electrolytic tank and an electrolyte. The photoelectric unit is used for converting solar energy into electric energy, and providing required electrolysis voltage or current. The photothermal unit is used for converting the solar energy into heat energy, heating solid electrolyte to reach the molten state, and heating the electrolytic tank to the electrolysis temperature. The electrolyte is mixture of molten carbonate and molten hydroxide, or mixture of molten carbonate and molten oxide, or mixture of molten carbonate, molten hydroxide and molten oxide. In the electrolysis, the electrode current is 0-3 A, the electrolytic cell temperature is 600 degrees C and carbon dioxide/water is regenerated by rlectrolyte absorption of air. An INDEPENDENT CLAIM is also included for high-temperature electrolysis of carbon dioxide/water to prepare a synthesis gas using the system, comprising (i) taking an electrolysis unit comprising photoelectric cell, cathode, anode, and electrolyte; (ii) heating and carrying out electrolysis of solid electrolyte in the photothermal unit to form a molten electrolyte; (iii) controlling the electrolytic cell temperature at 600-800 degrees C; and (iv) introducing carbon dioxide and water into the electrolytic cell through airway tube, controlling the direct current power supply of 1-2A, and reacting for 1-2 hours, where the main product synthesis gas is carbon monoxide and hydrogen, the main reaction as follows: carbon dioxide and water reacts to form carbon monoxide, hydrogen and oxygen, the intermediate product elemental carbon and hydrogen are generated in side reaction, the elemental carbon generation and reduction of carbon dioxide/water to form carbon monoxide/hydrogen as follows: carbon dioxide is converted to carbon and oxygen, one molecule of carbon and one molecule of carbon dioxide reacts to form two molecules of carbon monoxide, and carbon and water reacts to form hydrogen and carbon monoxide, and the electrolysis of water to generate hydrogen and reduction of hydrogen and carbon dioxide to carbon monoxide as follows: water is converted to hydrogen and nascent oxygen, and hydrogen and carbon dioxide reacts to form carbon monoxide and water.