The invention discloses a preparation method of wood gas. The preparation method comprises the following process of heating biomass to 900 to 1,100 DEG C in a condition that oxygen is isolated, and collecting a generated gas. The preparation method has the following advantages that the wood gas is prepared by directly performing the high-temperature pyrolysis on the biomass, and the obtained wood gas is high in combustion value and few in residue, and does not pollute an environment.