  The energy released from dark matter annihilation leads to additional
ionization and heating of the intergalactic gas and thereby impact the hydrogen
21-cm signal during the cosmic dawn. The dark matter annihilation rate scales
as density-squared and it becomes inhomogeneously boosted along with structure
formation. This paper examines the inhomogeneity in DM annihilation rate
induced by the growth of DM halo structures, and we show that this effect can
significantly enhance the spatial fluctuations in gas temperature, gas
ionization fraction and consequently the 21-cm brightness temperature. Compared
to previous homogeneous calculations, inhomogeneous dark matter annihilation
can enhance the 21-cm power spectrum by orders of magnitude across the scales
of $k \in [0.05, 3]\ {\rm{Mpc^{-1}}}$. For a DM annihilation rate of
$\left<\sigma v\right>/m_\chi \sim 10^{-27} {\rm cm^3 s^{-1} GeV^{-1}}$, the
corresponding signatures in the 21-cm power spectrum signal can be detected by
upcoming radio observatories such as the SKA.
