In this paper,the effect of RE elements on microstructure of Al-10Sr master alloy and the application in Al-20Si alloy casting was investigated. The experimental results revealed that: 1) the microstructure of Al-10Sr master alloy mainly containedα(Al) matrix and Al₄Sr phase; 2) The morphology of the Al₄Sr phase on Al-10Sr master alloy changed from acicular shape to small blocks with the addition of RE to 4.0wt %; 3) The grain size of primary silicon on Al-20Si alloy was refined into a range of 13.81-37.61μm, and the average grain size was 24.58μm with a homogeneous distribution during modification by using the Al-10Sr-4RE master alloy; 4) It was found that after adding RE, the Al₄Sr phase distribution became more homogeneous, and it exhibited better modification effect on Al-20Si alloy.