A 2-D model of fluidized bed was developed to study biomass particles gasification. Mass, momentum and energy conservations of gas were considered. Biomass particles pyrolysis was based on a one-stage mechanism, and species transport mechanism was developed for homogeneous and heterogeneous reactions of gas and solid. The particle motion, gasification and effects of temperature and equivalent ratio on gas composition were investigated, and the results were compared with experimental results. The results showed that the total time of the particles in gasifier was about 2.15 s, and particles fluidization became stable in 0.8 s. The mole fractions of CO2 and CH4 decreased along y axial, while CO and H2 had the opposite trend. Under different temperatures and equivalent ratios, the simulation mole fractions of H2, CO, CH4 and CO2 agreed sufficiently well with the experimental dates.