Abstract: The distribution and optimization of flow field is one of the key points for the scale up of magnesium electrolyzer. The distribution of flow field in magnesium electrolyzer under electromagnetic field is studied by CFD stimulation, and the distribution under currents of 120 kA was obtained. There exist major electrolyte circulations between electrolysis compartment and collection compartment, which can transport liquid magnesium from electrolysis compartment to collection compartment. There are minor electrolyte circulations near the back wall, which have scouring effects on back wall and anodes and damage them. The most optimum transport circulation of electrolyte is found at the midline of the electrolyzer which parallels with the electrode surface through analyzing the electrolyte circulations′ effect to the transportation in the electrolyzer. Meanwhile, there exist harmful circulations on the top of cathodes which are perpendicular to the surface of electrodes, and the maximum speed appears at the partition wall surface in electrolysis compartment by calculation. 0Refs. In Chinese.