Abstract: The effects of rare earth Sm on the microstructure, mechanical properties and thermal conductivity of Sr/B compound modified A356 aluminum alloy were investigated by OM, SEM, XRD, thermal conductivity meter and tensile testing machine. The results indicate that the addition of proper rare earth element Sm has good refinement and modification effect on the Sr/B compound modified A356 aluminum alloy. When 0.6% Sm is added to the alloy, the metamorphism effect is the most obvious, and compared with those of the sample without Sm addition the average size of secondary dendrite arm spacing is reduced from 14.3 μm to 9.6 μm; the average grain size of the α-Al primary phase is reduced from 64.9 μm to 42.4μm. At this time, the mechanical properties of the alloy also reaches the best, the tensile strength and elongation are 203.7MPa and 8.4%, which are improved by 20.6% and 95.3% compared with those of the sample without Sm addition,respectively; the thermal conductivity of the alloy is 159 W/（m·K）, and the mechanical properties and thermal conductivity of the alloy are higher than those of commercial A356 aluminum alloy.