Abstract: Stirred tanks are widely used in many industrial processes. In this paper, the mixing process of industry crystallizer was simulated three-dimensionally by computational fluid dynamics (CFD). The multireference frame (MRF) and standard k-ε turbulent model were used in the simulation to analyze the effect of the propeller structure, rotational speed and the distance of impeller location on the flow field in the crystallizer. The simulation results show that the velocity distributes mainly on the area in the interior draft tube and between the interior and exterior draft tube. Therefore, according to the notable difference of velocity at different areas, the crystallizer can be divided into approximately two zones based on the different effects in the flow processes of crystallization：the cycle zone with high velocity speed inside the draft tube and the sedimentation zone with low velocity speed outside the draft tube. Through comparison of velocity contour between cycle zone and sedimentation zone, propeller is proved to be more suitable than others, and the best distance of impeller location in the system is from 3.5 m to 5.7 m. The uniform velocity rate of fluid flow upward at the sedimentation zone engendered through the appropriate rotational speed can bring out the small crystals and is favorable for large particle size products. The detailed flow field in the stirred tank and different operation parameters can provide theoretical guidance to optimize the structure and operation parameter in the industrial scale. The industrial results show that the product particle size has been significantly increased, and the proportion of particles more than 0.2 mm increases from less than 50% to more than 90%. Natural gas consumption for drying products is decreased from 22 m3/t to 15 m3/t. The energy is remarkable saved.