Based on the Eulerian-Lagrangian framework, a reactive multi-phase particle-in-cell (MP-PIC) method is used to simulate biomass gasification in a three-dimensional pilot-scale dual fluidized bed (DFB) with complex geometric structure. After model validation, the optimal parameters for the simulation are derived via the independence tests. Thermochemical behaviors of bed materials and biomass particles are explored and the effects of temperature, steam-to-biomass ratio, and equivalence ratio on gasification performance are unveiled. The results show that the tendency of gas and solid temperature is opposite in the gasifier and combustor. The DFB can effectively control temperature, showing an excellent circulating and heat transfer feature. The pressure gradient distribution is highly related to the solid holdup distribution. Higher temperature and steam-to-biomass ratio increase lower heating value (LHV) and combustible gas concentration, resulting in the enhancement of gasification performance. Higher equivalence ratio decreases the LHV and combustible gas concentration, giving rise to a negative influence on the gasification performance. (C) 2020 Elsevier Ltd. All rights reserved.