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The electric pulse modification (EP, EPM) of liquid metal is a novel method for grain refinement. In this work, the structure of EP-modified Al-5％Cu melt was characterized by using high-temperature X-ray diffractometer. The results show that the Cu-containing Al clusters remarkably increase in the EP-modified melt, as the first peak of structure factor curve exhibits an obvious reduction. Furthermore, these clusters in that case trend to contract due to the decreases of relevant atomic radius and the co-ordination number. This kind of liquid-phase structure leads to a more homogeneous Cu-rich phase distribution in the final solidification structure. Differential Scanning Calorimetry (DSC) tests indicate the solidification super-cooling degree for the EP-modified liquid phase is 2.36 times than that of the unmodified. These facts suggest the atom cluster changes in EP-modified Al-5％Cu melt would be disagree with Wang’s postulated EPM model proposed in liquid pure metal.