Based on the first-principle, all geometric structures of Bn and BnNi clusters with n=6—12 have been optimized by using density functional theory with generalized gradient approximation, the equilibrium geometries for different spin multiplicities and ground-state structures have been determined. The results of Bn clusters are in good agreement with previous conclusions. When the Ni atom is doped in Bn clusters, the ground-state structure of the BnNi clusters favor three dimensional, but B12Ni cluster has the planar structure. The spin multiplicity of ground-state structures, except for n=8, obey the 2 and 1 alternate rule. The average atomic binding energies (Eb), second-order energy differences (Δ2E) and the HOMO-LUMO (gap) of ground-state structures have been calculated and discussed. The results indicated that n= 8 is the magic number of BnNi(n=6—12) clusters, implying that B8Ni cluster possess relatively higher stability. Calculated results on the magnetic moments show that the magnetic moment of B8Ni cluster is the biggest (2μB), the total magnetic moment and the average magnetic moment of clusters show the odd-even oscillation tendency along with the size increasing, and the magnetic moment is mainly provided by the 3 d orbital of Ni atom.