Abstract: In order to get aluminum-silicon alloys with low thermal expansion and high thermal conductivity, the effects of different Cu and Mg contents added to an Al-20Si alloy were investigated. The results showed that in the Al-20Si alloy, as the Cu content increased, the coefficient of thermal expansion, thermal conductivity, and electrical conductivity of the alloy all exhibited a decreasing trend, while the microhardness gradually increased. In the Al-20Si-2Cu alloy, as the Mg content increased, the coefficient of thermal expansion and the hardness showed an increasing trend, while the thermal and electrical conductivities decreased. When the Cu content was 2% and the Mg content was 0.3% in the Al-20Si alloy, a low-expansion, high-thermal-conductivity aluminum-silicon alloy with an expansion rate of 18.81×10^-6 K^-1 and a thermal conductivity of 132.55 W/(m·K) was successfully prepared.