Biomass gasification with steamoxygen enriched air in an atmospheric fluidized bed gasifier was studied. The gasifier was 9m high with the bed diameter of 0.5m. Sawdust with different moisture contents was used as feedstock, and it was fed into the gasifier at flow rates of 180～270kg/h. The effects of equivalence ratio, steam to biomass ratio, secondary flow ratio and feedstock moisture on the bed temperature, gas compositions, tar content, lower heating values, gas yield, carbon conversion efficiency and cold gas efficiency were investigated. The results showed under the operating conditions of ER is 0.25～0.27 and S/B=0.4, the following syngas was obtained: H2 content of 28.7%, H2/CO ratio of 0.94, low heating value of 9.9MJ/m3, cold gas efficiency was more than 75%, carbon conversion efficiency was more than 97%; a second flow ratio of 25% at the ER of 0.29 can significantly reduce the tar content to 49mg/m3, but hardly improve the quality of the gas produced; the rise of the feedstock moisture content caused a significant increase in CO2 content and a reduction in H2 and CO contents, and the moisture content is expected not to exceed 20%. 