A method for pyrolysis and gasification of biomass by: a) providing a gasifier and a pyrolysis furnace; heating and introducing a solid particle, or a plurality thereof, into the gasifier and the pyrolysis furnace; b) grinding and feeding the biomass into the pyrolysis furnace while spraying saturated water vapor into the pyrolysis furnace, contacting the biomass with the saturated water vapor at 500-800° C. to yield crude synthetic gas and ash including coke; c) separating the ash, heating the solid particle, and transporting the solid particle into the gasifier; d) cooling the ash, and separating the coke; and e) introducing the crude synthetic gas into the gasifier, transporting the coke into the gasifier while spraying saturated water vapor into the gasifier, contacting the coke and the crude synthetic gas with the saturated water vapor at 1200-1600° C.