Abstract: In the present work, the Eulerian–Eulerian method is used to simulate a laboratory-scale coaxial entrained flow gasifier in Brigham Young University. The gas turbulence in the reactor is modeled by the k-ε turbulent model, and the particle phase is modeled with the kinetic theory of granular flow (KTGF). In the simulation of turbulent chemical reaction flow, three heterogeneous reactions and five homogeneous reactions are considered. For thermal energy equilibrium, the P-1 radiation model is coupled with the transport equation of energy. Different from conventional Eulerian model, in this work the gradient-diffusion model is introduced to modify the particle distribution because of turbulent diffusion. Furthermore, it is considered the diameter of solid fuels is changing during the gasification. Therefore, a new variable and its transport equation are implemented to capture the coal particle diameter change in this simulation. All submodels above are integrated and realized in the open-source software MFIX. The simulation results have a good agreement with the experimental measurements, and the carbon conversion in the simulation is 82.8 %.