  Expanding X-ray halo or rings appear when short pulses of X-ray radiation
from a background source are scattered by clouds of dust in the Milky Way. We
study the X-ray rings of the brightest gamma-ray burst (GRB) 221009A, detected
by the {\it Swift} X-Ray Telescope. The rings center on the GRB position and
their angular radii increase with time. We identify five major expanding rings,
and our modeling of their expansion history suggests that they are scattered
off, respectively, from five dusty clouds at distances of 0.4-13 kpc from the
observer. Given an assumed prompt X-ray fluence of this GRB, the fluxes of
those rings suggest that these clouds have dust grain column densities of
$10^{7\sim8}~\mathrm{cm^{-2}}$. More interestingly, our time-dependent spectral
analysis of these rings show that they all experience spectral softening, i.e.,
getting softer as they expand, with spectral indices ranging from 2.2 to 5,
consistent with what the dust scattering model predicts.
