The reactor of an industrial methanol to olefins (MTO) unit is a large turbulent fluidized bed reactor with a dense phase section diameter of 10 m, which has a plate gas distributor at the bottom and double-layer mesh grids in the dense bed. In this study, MP-PIC (multi-phase particle-in-cell) method was used to simulate the hydrodynamics of this industrial reactor proportionally. All the major internals such as particle distributors, mesh grids, and cyclone separator groups were considered in the simulation, and main operating parameters were taken from industrial data to study the role of double-layer mesh grids in the reactor. The results show that the average bed density obtained by simulation is in good agreement with the actual industrial data. The installation of double-layer mesh grids increases the height of the dense phase bed and reduces the average density of the dense phase bed by 112 kg/m³, indicating the improvement of the fluidization quality and gas-solid contact efficiency of the dense phase bed. Mesh grids can effectively limit the generation of large bubbles in the bed, so that the dense phase particles above the grid are more evenly distributed and the gas-solid mixing is more sufficient. Meanwhile, the axial back-mixing of particles in the dense phase zone of the reactor can be greatly inhibited.