Abstract: SiCp/AZ91D magnesium matrix composites were prepared under four kinds of external field conditions: normal condition, electromagnetic simulated microgravity field condition, pulse current field condition and "electromagnetic simulated microgravity + pulse current" condition. The test results indicate that: In the normal condition, the grain size of the sample is coarse, the β-Mg₁₇Al₁₂ phase shows an irregular grid structure, and Mg₂Si exists in the granular primary phase and dendritic eutectic phase. In the electromagnetic simulation microgravity field condition, the β-Mg₁₇Al₁₂ phase transforms into short rods and granules, and Mg₂Si is transformed into patterned eutectic phase. In the pulse current field condition, the β-Mg₁₇Al₁₂ phase transforms into regular distribution of rectangular grid, and Mg₂Si exists in dendritic eutectic phase with obvious directivity. The "electromagnetic simulated microgravity + pulse current" condition combines the advantages of the first two kinds of external field conditions, the grain size of the sample is obviously refined, the β-Mg₁₇Al₁₂ phase presents granular, short rod and rectangular grid structures and the Mg₂Si is transformed into the pattern and dendritic eutectic structure throughout the grain. Compared with the sample under normal condition, the microhardness is improved by 25.1% and the friction property is improved by 31%.