Three kinds of Al-Si piston alloys were prepared and subjected to pulse electric current treatment (PECT) at different pouring temperatures. Some aspects of the solidification microstructures were examined including the morphology and the distribution of the matrix and the secondary phases by using of optical microscopy (OM), SEM and EDS methods. Results indicate that PECT can refine the grains of α-Al in the alloys as effectively as chemical modification by sodium salt. The processing parameters of PECT on the multi-component Al-Si alloys were then optimized through the testing of tensile strength, elongation and microhardness of the prepared alloys. A new theory was put forward to explain the mechanism of PECT.