Abstract: Molten Sn-15%Pb alloy, which was used as the test material, was treated with electric pulse for different treating time under the condition of 90℃ overheating. The modifying effects on solidification process and structures were investigated by thermal analysis and solidification structure observation. The results showed that the solidification structures of Sn-15%Pb alloy were changed significantly after electric pulse modifying. The morphology of primary crystal enriched Sn changed from dendrite to cellular. Corresponding with the changing of solidification structures, the cooling curves were changed significantly. The lowest temperature of primary crystallizing increased in a rather large range. With the increasing of electric pulse process time, the amount of cellular primary crystal changed periodically, that is little, large, little, large. At the same time, the lowest temperature of primary crystallizing also changed periodically with the extension of electric pulse treating time.