Density functional theory B3LYP are performed in study on structure of Ni_n,Ni_n⁺ and Ni_n^-(n=2-8).DGDZVP all-electron basis sets and TZVP all-electron basis sets are employed. Equilibrium geometries, ionization potentials,electron affinities and binding energies are obtained.It shows that the ground state of Ni₂,Ni₃,Ni₄,Ni₅ and Ni₆ cluster are 5-,7-,9-,11-,and 13-multiple state,respectively,which indicates spin polarization effect in Ni_n (n≤8 )clusters is important.That is,there are 4,6,8,10,and 12 parallel spin electrons iu Ni₂,Ni₃,Ni₄,Ni₅ and Ni₆ cluster,respectively.Number of non-conjugated electrons in ground state cluster is the greatest.These electrons occupy different spacious orbitals so that energy of Ni_n (n≤8) cluster is minimized.It can be concluded that effect of parallel spin in Ni_n (n≤8) clusters is greater than effects of conjugated clusters,which is obviously related to electron d delocalization.This is spin polarization effect of Ni_n (n≤8) clusters,which is a result of the Hund' s rule.Moreover,we find that spin magnetic moments of Ni_n(n=6-8) are 8 μ_B,those of Ni_n⁺(n=6-8) are 9 μ_B and those of Ni_n^-(n=4-10) are7 μ_B.