Abstract: Magnesium alloys have been widely applied in various fields due to their excellent properties, while inclusions existing in the melt can severely deteriorate the performance of final products. Based on the computational fluid dynamics simulation method, the influence laws of pore size (0.6-4 mm) and thickness (5-25 mm) of MgO ceramic filters on the inclusion capture behavior in magnesium alloy melts were systematically investigated. The results show that the capture rate of 100 μm inclusions is continuously improved with the decrease in filter pore size, whereas the capture rate of 20 μm inclusions increases first and then tends to be stable, and the pressure difference across the filter increases continuously with the decrease in pore size simultaneously. Considering the purification performance and the demand for low pressure difference comprehensively, 1 mm is determined as the optimal pore size. In terms of the influence of thickness, the capture rate of 20 μm inclusions reaches the peak (33.8%) when the filter thickness is 15 mm, and the inclusion convergence effect in front of the inlet is the most significant, while the distribution of 100 μm inclusions is hardly affected by the variation in thickness. At a constant melt flow rate of 0.2 m/s, the thickness exerts a slight influence on the melt residence time and flux, but the pressure difference across the filter increases linearly with the increase in thickness, and this variation law is consistent with the Ergun equation. By comprehensively considering the purification efficiency and operation energy consumption, the MgO ceramic filter with a thickness of 15—20 mm and a pore size of 1 mm is recommended, and the synergistic optimization of high-efficiency purification and low-pressure-difference operation of magnesium alloy melts can be achieved accordingly.