Abstract: The characteristics of biomass gasification with oxygen-steam mixtures in a fluidized bed are studied in this paper. The effects of feedstock, equivalence ratio (ER), steam to biomass ratio (S/B), gasification temperature, secondary oxygen supply and bed materials on gasification performance were investigated. The results showed that higher C and H content of feedstock was more favorable for higher H₂ and CO content and lower tar content of fuel gas. The H₂ content increased with gasification temperature and reached its maximum at ER=0.27 and S/B=0.6. Higher gasification temperature (>840 ℃) also contributed to higher CO content. The introduction of secondary flow upper the feedstock inlet with a second flow ratio of 15% improved the gas quality significantly, and more tar was reduced as the secondary flow inlet move upward the gasifier. Dolomite and limestone performed better than olivine on cracking tar and increasing H₂ content, but resulted in higher ash content.