NOVELTY - Preparing biomass fuel gas comprises putting biomass into gas generating chamber, pyrolyzing, which forms mixed gas; cracking tar in the mixed gas to product combustible gas; removing fly ash in the combustible gas by filtering; separating water and gas; and eliminating odor.    USE - The method is useful for preparing biomass fuel gas (claimed).    ADVANTAGE - The method and device can efficiently remove tar, fly ash, steam and odor in the biomass fuel gas, does not pollute environment and ensures combustion thermal efficiency of the fuel gas.    DETAILED DESCRIPTION - Preparing biomass fuel gas comprises putting biomass into gas generating chamber, pyrolyzing, which forms mixed gas; cracking tar in the mixed gas to product combustible gas; removing fly ash in the combustible gas by filtering; separating water and gas; and eliminating odor, where the process flow comprises pyrolyzing, cracking tar, removing water, eliminating odor; specifically putting biomass into gas generating chamber, pyrolyzing, which forms mixed gas; cracking tar in the mixed gas repeatedly to product combustible gas, removing fly ash in the combustible gas by filtering, removing water primarily by water retaining sorbent, keeping heat of cracking catalyst below it to raise temperature of the cracking catalyst to cracking temperature of tar, which cracks the tar, where when temperature increases to the points which makes hydrophobic nature of the water retaining sorbent appear, steam in the gas is stopped by the water retaining sorbent and changed into water, and the water flows downwards by gravity to brush tar and fly ash on cracking layer, so that the tar and fly ash gets into biomass, and material with tar moves downwards continuously to high temperature cracking area; repeating the processing; eliminating odor of the gas primarily by odor reducing filtering agent; step three includes step of: separating water from the gas treated by step two, which removes residual water; eliminating odor of gas treated, and the gas can be used after the odor is eliminated. An INDEPENDENT CLAIM is a device for preparing biomass fuel gas comprising pedestal (1), gas generating chamber (2), storage compartment (3), catalytic cracking absorber (4) , water/gas separator (5), odor reducing gas tank (6), where the gas generating chamber is fixed on pedestal, storage compartment is fixed on upper side of the gas generating chamber, catalytic cracking absorber is fixed on upper side of the storage compartment and connected to the storage compartment, the catalytic cracking absorber is connected to water/gas separator through pipe, and the water/gas separator is connected to odor reducing gas tank through pipe.    DESCRIPTION OF DRAWING(S) - The drawing shows a front view of the device for preparing biomass fuel gas.    Pedestal (1)    Gas generating chamber (2)    Storage compartment (3)    Catalytic cracking absorber (4)    Water/gas separator (5)    Odor reducing gas tank (6)