The evolution of liquid metal at high temperature is known much less than their solid states. This is partially due to that the message concing clusters, metastable phase or heterogeneity in liquid is usually too slight to be traced. Here, we shed some light on the nature of structural evolution of Fe-based glass-forming alloy during overheating process by the investigation of high-temperature melt viscometry and first principles simulations. It was found that a structural transition around 1400℃occurred in the melts of initial homogeneous ingot, het-erogeneous ingot and amorphous ribbons jointly, and was confirmed by the results from differential scanning calorimeter (DSC), and ab initio molecular dynamics (AIMD). Combining these results with Fe-Si-B tary phase diagram and the melting characteristics of Fe-B compounds, it is safe to conclude that the disintegration of Fe2B-type clusters to Fe3B-type clusters leads to the observed transition. These results offer a significant reference for the preparation and property control of Fe-based amorphous alloys.