A 3D computational hydrodynamics model (CFD) of a two-stage entrained-flow biomass gasifier is developed for further engineering application of the clean utilization of renewable energy. The biomass gasification procedure in the entrained-flow gasifier is simulated with the CFD software FLUENT (R) 15.0. The Eulerian-Lagrangian method is applied to model the two-phase chemical reaction and heat transfer flow. Based on the multi-step chemical reaction dynamics, the homogeneous and heterogeneous biomass gasification reaction are described, respectively. The realizable k-epsilon model describes the turbulent flow of gas phase, and the motion of pulverized-biomass particles is tracked by the stochastic tracking method (STM). Using steam-air as gasification agent, different reaction mechanisms are simulated to compare with the verification value to find the optimal reaction mechanism. Then the quantitative influence of the main parameters of biomass gasification, namely, different equivalent ratios (ER), steam-to-biomass mass ratios (S/B), and the distribution ratios between the upper and lower stages (DR) are studied with the orthogonal analysis method. The results show that the proper values of ER, S/B and DR are helpful to improve gasification performances, such as maximum flame temperature, syngas compositions, active components, carbon conversion rates, etc. The optimum parameters for gasification condition are found as S/B = 0.1, ER = 0.16, DR = 30%/70%. (C) 2020 Elsevier Ltd. All rights reserved.