  Black holes are extraordinary massive objects which can be described
classically by general relativity, and topological insulators are new orders of
matter that could be use to built a topological quantum computer. They seem to
be different objects, but in this paper, we claim that the black hole can be
considered as kind of topological insulator. For BTZ black hole in three
dimensional $AdS_3$ spacetime we give two evidences to support this claim: the
first evidence comes from the black hole "membrane paradigm", which says that
the horizon of black hole behaves like an electrical conductor. On the other
hand, the vacuum can be considered as an insulator. The second evidence comes
from the fact that the horizon of BTZ black hole can support two chiral
massless scalar field with opposite chirality. Those are two key properties of
2D topological insulator. We also consider the coupling with the
electromagnetic field to show that the boundary modes can conduct the
electricity. For higher dimensional black hole the first evidence is still
valid. So we conjecture that the higher dimensional black hole can also be
considered as higher dimensional topological insulators. This conjecture will
have far-reaching influences on our understanding of quantum black hole and the
nature of gravity.
