Compression tests on semi-solid SiCp/AZ61 magnesium matrix composites were carried out using Thermecmastor-Z dynamic material testing machine.Influences of strain-rate,strain,temperature and volume fraction of SiC particles on flow stress were analyzed.The results show that the flow stress of semi-solid SiCp/AZ61 composites is sensitive to temperature and strain rate.The lower the temperature and the larger the strain rate,the higher the flow stress.Meanwhile the flow stress increases with the increase of the volume fraction of SiC particles.This study helps establish the constitutive model of magnesium matrix composites and offers theoretic and experimental references for its thixoforming.