  Based on a two-orbital model and taking into account the presence of the
impurity, we studied theoretically the electronic structure in the vortex core
of the iron-Pnictide superconducting materials. The vortex is pinned when the
impurity is close to the vortex core. The bound states shows up for the
unpinned vortex and are wiped out by a impurity. Our results are in good
agreement with recent experiments and present a consistent explanation for the
different electronic structure of vortex core revealed by experiments on
different materials.
