Biomass gasification is a promising technology for the utilization of biomass. In this study, a mathematical model for biomass gasification in dual fluidized bed (DFB) has been developed. The fluidized bed with biomass gasification was simulated as a bubbling fluidized bed, which was further divided into a bubble phase and an emulsion phase for modeling. The modeling results were compared with the experimental data to be in high agreement. The in fluences of steam to biomass mass ratio (S/B) and gasification temperature on the performances of the product gas concentration, the CO/H-2 and CO2/CO molar proportions were focused on.