A computer simulation tracking study for the rapid solidification processes of liquid metal In system has been performed by means of molecular dynamics method.U sing the index method of HoneycuttAndersen(HA)and the cluster bondtype index method,the bondtypes,clusters and cluster configurations of In atoms are anal yzed.It has been found that,contrary to conventional metals(such as Al),the rela tive number of 1551,1541 bond types,related to the icosahedral configuration,is decreased remarkably with decreasing temperature;the total number of 1421,1422 a nd 1431 bond types,related to the fcc and hcp structures,only changes a little;t he total number of 1321,1311,1301 and 1201 bond types,related to the rhombohedra l structure,increases remarkably,and then gradually plays a dominant role.Finall y,the amorphous structure is formed mainly with rhombohedral structures and mixe d up with clusters of cubic(fcc,bcc)and hcp structures.However,the icosahe dral and various polyhedra structures,which occupied a dominant position in the previous amorphous structure of metal Al,vanish completely in the present amorph ous structure of metal In.This is just the physical origin in microstructure for the obvious difference between the g(r) curves of amorphous In having a spl itting second peak with a lower front subpeak and a higher behind one,and the g(r) curves of amorphous Al having a splitting second peak with a higher fro nt subpeak and a lower behind one.