To understand the behavior of the down-flow gasifier for woody biomass, the optimum operation conditions and gasification characteristics were studied. Pulverized wood powder sieved to under by 60 mesh was used for gasification fuel. The CO2 concentration was increased by 10% by the promotion of oxidation at temperatures above 1600 K. However, total production of CO and H-2 showed little change at around 60%, comprising 40% of CO and 20% of H-2 in the total flue gas. CH4, C2H2 and C2H4 were under 5%, 2%, 2%, respectively under the same conditions. Therefore, combustible gas (CO+H-2+CH4) was over 60%, and the gas-heating value was 5.9-8.9 MJ/m(3) N. Carbon gasification conversion and cold gas efficiency reached 90% and 50% respectively at the temperature of 1600 K. Choking of the bag filter by biomass tar was controlled better by injecting on inert absorbent.