Stir casting process are well suited for large scale and complex composite components,but the flow behavior becomes complex due to the addition of SiC particles, therefore the mould filling process becomes the key factors of preparing high quality composite castings. In this study, the flow model of SiCp/A357 composites was built through numerical method, and the fluidity and SiC particle distribution were tested with fluidity test. The results showed that numerical simulation was roughly accord with fluidity test. The fluidity of SiCp/A357 composites increased with pouring temperature, which was more obvious in semi-solid state. The volume fraction of SiC particles at the flow-front was lower than the end, the whole homogeneity of SiC particles decreased, this tendency intensified with pouring temperature increasing. The fluidity of SiCp/A357 composites decreased with volume fraction. With volume fraction increasing, the tendency of SiCp reduce at flow front slowed, the homogeneity of SiCp inproved.