A one-dimensional model is built based on the commercial Aspen Plus software to kinetically simulate the biomass/coal co-gasification process in a dual fluidized bed gasifier. The synergistic effect on the co-gasification kinetics is allowed for, and is coupled with the gas-solid flow hydrodynamics. With the developed model, the effects of different key operating parameters including the biomass blending ratio (R-b), the initial bed temperature (T-g), the feedstock mass flow rate (F-fs), the bed material flux (F-bm) and the steam to carbon ratio (R-sc) on the resultant syngas composition and the supplemental fuel mass flow rate (F-sf) are investigated, and the operation parameters are optimized. It is found that increasing R-b and T-g can enhance the gasification, while increasing F-fs and Rsc restricts the gasification. Increasing F-bm has slight effect on the gasification results but can reduce F-sf. The cold gas efficiency is up to 78.9% under the proposed optimum condition.