A method for producing synthesis gas, including: 1) pre-processing a biomass raw material; 2) pyrolyzing the biomass raw material to yield a pyrolysis gas and a carbon powder; 3) separating the pyrolysis gas from the carbon powder and a solid heat carrier; 4) separating the carbon powder away from the solid heat carrier via a solid-solid separator; 5) conveying the generated pyrolysis gas to a condensate tank for spray condensation, condensing a condensable part in the pyrolysis gas to generate biological fuel oil, pressurizing the generated biological fuel oil by a high pressure oil pump and feeding to a gasification furnace to be gasified; and 6) feeding one part of non-condensable pyrolysis gas to a combustion bed to combust with air, and conveying the other part of the non-condensable pyrolysis gas to the pyrolysis bed as a fluidizing medium.