Formation of icosahedral clusters in rapidly solidified binary amorphous NixZr100-x (x = 15, 33.3, 50, 66.7, 85) is studied by using molecular dynamics simulation methods. A large number of icosahedral clusters with 13 atoms (Ih13) were observed in NixZr100-x alloys, and most of them, even those in Zr-rich alloys, are found to be Ni-centred. Studies on the structures of Ni33.3Zr66.7 obtained at different cooling rates demonstrate that most of iscosahedral clusters enhanced by decreasing cooling rates are also Ni-centred. The essentials of Ni atoms preferring to be the core of icosahedral clusters are illustrated with the criterion of energy minimization and the equilibrium interatomic distances between different atoms.