Abstract: In this paper, a reactive MP-PIC model is built on the open-source software package OpenFOAM to explore biomass gasification in a fluidized bed reactor. In this model, gas phase is solved under Eulerian frame while solid phase is regarded as Lagrangian computational particles. The general flow patterns, gas-solid fluxes, distribution of syngas composition, and effect of operating parameters on gasification performance are both qualitatively and quantitatively analyzed. The results show that biomass particles are inclined to migrate and concentrate at the bed surface. Profiles of vertical gas fluxes show a single peak distribution while profiles of vertical solid fluxes present a “W” shape. The heterogeneous reactions mainly occur at the bed surface while the homogeneous reactions mostly take place above the bed surface. Higher temperature enforces the endothermic reactions for products formation. Increasing steam/biomass ratio increases H2 and CO2 formations but decreases CO formation. The four types of feedstock show a similar gasification performance with little variation in the syngas composition. As a priori test, it is demonstrated that the proposed model is reasonable to be used to investigate gas-solid hydrodynamics and reactive characteristics of biomass gasification in fluidized bed reactors.