First-principles calculations have been used to research the electronic structure and magnetic properties of zigzag boron nitride nanoribbons(ZBNNRs) terminated/jointed by armchair dimer-Fe chains(respectively called Fe-terminated ZBNNRs and Fe-jointed ZBNNRs).The Fe-terminated ZBNNRs is a semiconductor for different ribbon widths,and the Fe-jointed ZBNNRs become half-metallic regardless of the ribbon width.The magnetism of both structures mainly stems from the Fe atoms.It is found that the self-metallicity of the Fe-jointed ZBNNRs results from the strong interaction between the 3d orbitals of Fe atoms and the 2p orbitals of N atoms.The stability of the Fe-jointed ZBNNRs under room temperature has been confirmed by molecular dynamics simulation.This kind of half-metal property means a selectivity for the two different electrons,it can be applied to spintronics devices.Other transition-metal jointed ZBNNRs are also studied,which can be metals,half-metals or semiconductors with different ground states.