The effects of the content of Cu and Si elements as well as heat treatment on the lattice constant and electrical properties of Al-Si alloys were investigated by Wheatstone bridge conductivity measurement, optical microscope, scanning electron microscope and X-ray diffraction analysis. The results indicate that increasing the content of Si and Cu can decrease the conductivity of Al-Si alloy. When Si content is larger than its solubility in Al, variation of Si content has less influence on the lattice constant, and the resistivity of Al-Si alloy is determined by the volume percentage of Si. When Cu content is within its solubility in Al, the increase of Cu content would increase the distortion of aluminum lattice; consequently, the influence of Cu can be estimated according to Al lattice constant deviation. After heat treatment (450 °C×5 h+250 °C×2 h), the distortion of the matrix lattice decreases significantly, and the electrical conductivity of Al-Si alloys improves obviously with the increment up to 32%.