Phase-change materials based on chalcogenide alloys have been widely used for optical datastorage and are promising materials for nonvolatile electrical memory use. However, themechanism behind the utilization is unclear as yet. Since the rewritable data storageinvolved an extremely fast laser melt-quenched process for chalcogenide alloys, theliquid structure of which is one key to investigating the mechanism of the fastreversible phase transition and hence rewritable data storage, here by meansof ab initio molecular dynamics we have studied the local structure of liquidGe1Sb2Te4. The results show that the liquid structure gives a picture of most Sb atomsbeing octahedrally coordinated, and the coexistence of tetrahedral and fivefoldcoordination at octahedral sites for Ge atoms, while Te atoms are essentiallyfourfold and threefold coordinated at octahedral sites, as characterized by partial paircorrelation functions and bond angle distributions. The local structure of liquidGe1Sb2Te4 generally resembles that of the crystalline form, except for the much lower coordinationnumber. It may be this unique liquid structure that results in the fast and reversible phasetransition between crystalline and amorphous states.