  Low mass galaxies are expected to be dark matter dominated even within their
centrals. Recently two observations reported two dwarf galaxies in group
environment with very little dark matter in their centrals. We explore the
population and origins of dark-matter-deficient galaxies (DMDGs) in two
state-of-the-art hydrodynamical simulations, the EAGLE and Illustris projects.
For all satellite galaxies with $10^9<M_*<10^{10}$ M$_{\odot}$ in groups with
$M_{200}>10^{13}$ M$_{\odot}$, we find that about $2.6\%$ of them in the EAGLE,
and $1.5\%$ in the Illustris are DMDGs with dark matter fractions below $50\%$
inside two times half-stellar-mass radii. We demonstrate that DMDGs are highly
tidal disrupted galaxies; and because dark matter has higher binding energy
than stars, mass loss of the dark matter is much more rapid than stars in DMDGs
during tidal interactions. If DMDGs were confirmed in observations, they are
expected in current galaxy formation models.
