Abstract: Due to the advantages of high carbon conversion and high capacity, pressurized entrained flow gasification is of interest and becoming increasingly important in the production of synthesis gas. To improve the thermal efficiency, the entrained flow gasifiers often use twostage feeding mode. Recently, a novel pilot scale twostage entrained flow gasifier has been developed in China. In order to meet the requirements of the process development, a 3-D full scale(ID700mm×H11200mm) mathematics model based on the Computational Fluid Dynamic (CFD) has been developed for investigating the gassolid flow characteristics in the gasifier. In the model, the gas phase was treated as continuous phase with an Euler frame of reference, while the particle phase was modeled as dispersed phase with a Lagrange frame of reference. Base on this CFD model, a simulation was performed firstly under the base designing and operating condition, which gave the kinetics regulation of the gassolid twophase and the distribution of particle in the gasifier. And then a series of numerical simulations were performed under several different designing and operating conditions (the throat diameters and gassolid flow rate in the two stages) to investigate the effect of design and operation parameters on the gassolid flow throughout the gasifier. The results showed that throat diameter was critical in the twostage entrained flow gasifier, which might control the flow field, particle trajectory and particle distribution. The smaller throat diameter leads to not only stronger gas recirculation near the throat, swirling particle trajectories but also obviously changing of the particle distribution. The changes of feeding rate between the twostage obviously influence the gas flow flied and particle behavior. The feeding rate increase in the first stage and the decrease in the second stage will enhance the gas recirculation in the first stage, weaken the recirculation in the second stage and leads to stronger particle swirling up movement, higher particle concentration near the wall and less particle deposition at the bottom.