  Cosmic-ray (CR) antihelium is an important probe for the indirect search of
dark matter (DM) annihilation in the Galaxy. However, due to stringent
constraints from the measurements of CR antiprotons and $\gamma$-rays, the flux
of CR antihelium from the conventional DM direct annihilation into Standard
Model final states is expected to be far below the sensitivity of the current
experiments. We show that the production of antihelium can be significantly
enhanced if the DM particles annihilate through light mediator particles with a
mass $m_\phi \approx 8$ GeV close to the antihelium production threshold. After
taking into account the constraints from the AMS-02 antiproton data and the
Fermi-LAT $\gamma$-ray data on the spheroidal dwarf galaxies, we find that in
this scenario the CR antihelium flux can be enhanced by three orders of
magnitude, which makes it within the sensitivity of the ongoing AMS-02
experiment.
