Abstract: In this paper, the biomass gasification process in a bubbling fluidized bed (BFB) reactor was numerically simulated by using computational fluid dynamics–discrete element method (CFD–DEM) coupled with thermochemical and poly-dispersed drag model. After model validation, the effects of key operating parameters on particle-scale information (e.g., particle motion, mixing, heat transfer) and reactor performance were discussed. The results show that in the process of biomass gasification, convective heat transfer plays a leading role, followed by radiative heat transfer and reaction heat. The proportion of conductive heat transfer is the smallest and can be ignored. Increasing the operating temperature can enhance heat transfer and reaction, and increase the temperature of biomass particles. Increasing biomass/steam ratio promotes gasification reactions, consumes more heat and reduces biomass particle temperature. The decrease of biomass particle temperature will increase the temperature difference between biomass particles and bed material particles, so as to increase the conductive, convective and radiative heat transfer.