A simulation study has been performed for the rapid solidification process of liquid Mg7Zn3 alloy by using molecular dynamics method. The pair distribution function g(r) curves, the bond-type index method of Honeycutt-Andersen (H-A), the cluster-type index method and the genetic tracking method have been used to analyze the formation and evolution properties of cluster structures during the solidification process. The results show that the bonding probability between Zn-Zn atoms is increased obviously during the solidification process at cooling rate of 1×1012 K ·s-1. The amorphous structures are formed mainly with the 1551, 1541 and 1431 bond-types, and the turning point of the relation curve of the characteristic 1551 bond-type with temperature is corresponding to the glass transition temperature Tg, thus it maybe become a new method to determine Tg. The basic cluster (12 0 12 0) consisting of 1551 bond-type plays a key role in forming amorphous structure, and becomes the main body of the large clusters which are formed by the combination of some middle and small clusters with distinctly different sizes, through mutual competition by unceasing annex and evolution in a seesaw manner (in turn of obtaining and losing).