NOVELTY - A device for producing synthesis gas by using urban domestic garbage and landfill gas comprises a landfill gas separation device, an updraught fixed bed, and an air stream bed; where the landfill gas separation device is connected with a landfill gas pipeline; the landfill gas separation device is set with a carbon dioxide outlet and a methane outlet; the updraught fixed bed is set with a trash feeding opening, a gasification agent inlet, a gas product outlet, and an ash residue outlet; and the air stream bed is set with gas inlet, gas outlet, and cooling chamber below the air stream bed.    USE - The device and the process are useful for producing synthesis gas by using urban domestic garbage and landfill gas (all claimed).    ADVANTAGE - The device synchronously considers recycle and utilization of both urban domestic garbage and existing trash landfill gas. Moreover, it is environment friendly, saves energy, and has high resource utilization rate.    DETAILED DESCRIPTION - A device for producing synthesis gas by using urban domestic garbage and landfill gas comprises a landfill gas separation device, an updraught fixed bed, and an air stream bed; where the landfill gas separation device is connected with a landfill gas pipeline; the landfill gas separation device is set with a carbon dioxide (CO2) outlet and a methane (CH4) outlet; the updraught fixed bed is set with a trash feeding opening, a gasification agent inlet, a gas product outlet, and an ash residue outlet; the air stream bed is set with a gas inlet, a gas outlet, and a cooling chamber below the air stream bed; the CO2 outlet and the oxygen (O2) outlet are connected with the gasification agent inlet; the gas product outlet and the CH4 outlet are connected with the gas inlet of the air stream bed; the gas outlet of the air stream bed is connected with a cooling chamber; the bottom of the cooling chamber is a cooling water tank; the gas outlet in the cooling chamber is set with a coolant nozzle; and the cooling chamber is set with a synthesis gas outlet. An INDEPENDENT CLAIM is a method for producing synthesis gas by using urban domestic garbage and landfill gas, comprising: (a) feeding urban domestic garbage into the updraught fixed bed, separating CO2 and CH4 from the trash landfill gas, mixing CO2 with O2, feeding into the updraught fixed bed, gasifying the urban domestic garbage in the updraught fixed bed, outputting the ash residue generated by gasifying the urban domestic garbage from the ash residue opening; (b) feeding the gasified gas generated by gasifying the urban domestic garbage and CH4 separated from the trash landfill gas, partially oxidizing and reforming the mixed gas at high temperature to generate chemical synthesis gas, feeding the synthesis gas into the cooling chamber; and (c) spraying coolant into the cooling chamber, making molten residue in the cooling gas fall into the cooling water tank, and outputting the cooled synthesis gas.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the device for producing synthesis gas by using urban domestic garbage and landfill gas.