NOVELTY - The outer wall of a clean gas cabinet corresponding to a mixed gas chamber is provided with a combined fuel gas inlet. The bottom of the mixed gas chamber is provided with an absorption purification layer composed of mineral materials. A clean gas chamber is set above a gas filter screen. The outer wall of the clean gas cabinet corresponding to the clean gas chamber is provided with a clean fuel gas outlet.    USE - Multi-functional biomass gasification device.    ADVANTAGE - Has wide variety of materials and reasonable hearth structure. Combustion chamber is in optimal pyrolysis state, and communicated annular gas channel and vertical gas channel make once generated fuel gas return and pass through combustion area for re-pyrolysis of and purifying coal tar. Gas generator and gas storage device are separated, fuel gas is filtered and purified by multiple layers, concentration of fuel gas is improved and impurities are reduced.    DETAILED DESCRIPTION - A cover encloses a water seal tank on the outer edge of the furnace top. The middle part of a gasifier has a pressure hole with a sealing cover. The hearth of the gasifier is a square cylindrical cavity with a flat bottom provided with a variable air head. An annular furnace inner wall at the upper end of the hearth is provided with an annular gas channel having a gas inlet. One side wall in the furnace is provided with a vertical channel from bottom to top and communicates with the annular gas channel. The bottom of the vertical gas channel opens to a gas inlet. The outer wall of the furnace from bottom to top is provided with a combined fuel gas chamber and a gas discharging valve communicating with the vertical gas channel. A combined fuel gas outlet is connected to the combined fuel gas inlet at the bottom of the clean gas cabinet whose interior is divided into two parts by the gas filter screen which is set in the middle. A micro-granular gas filtering agent is distributed on the gas filter screen. The mixed gas chamber is set below the gas filter screen.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the multi-functional biomass gasification device.