  We show that "particle production" by gravitational field, especially the
Hawking effect, may be treated as some quantum inertial effect, with the energy
of Hawking radiation as some vacuum energy shift. This quantum inertial effect
is mainly resulted from some intrinsical energy fluctuation $\hbar\kappa/c$ for
a black hole. In particular, there is an extreme case in which $\hbar\kappa/c$
is the Planck energy, giving a "Planck black hole" whose event horizon's
diameter is one Planck length. Moreover, we also provide a possibility to
obtain some positive cosmological constant for an expanding universe, which is
induced from the vacuum energy shift caused by quantum inertial effect.
