  The abundance of neutral hydrogen (HI) in satellite galaxies in the Local
Group is important for studying the formation history of our Local Group. In
this work, we generated mock HI satellite galaxies in the Local Group using the
high mass resolution hydrodynamic \textsc{apostle} simulation. The simulated HI
mass function agrees with the ALFALFA survey very well above $10^6M_{\odot}$,
although there is a discrepancy below this scale because of the observed flux
limit. After carefully checking various systematic elements in the
observations, including fitting of line width, sky coverage, integration time,
and frequency drift due to uncertainty in a galaxy's distance, we predicted the
abundance of HI in galaxies in a future survey that will be conducted by FAST.
FAST has a larger aperture and higher sensitivity than the Arecibo telescope.
We found that the HI mass function could be estimated well around $10^5
M_{\odot}$ if the integration time is 40 minutes. Our results indicate that
there are 61 HI satellites in the Local Group, and 36 in the FAST field above
$10^5 M_{\odot}$. This estimation is one order of magnitude better than the
current data, and will put a strong constraint on the formation history of the
Local Group. Also more high resolution simulated samples are needed to achieve
this target.

Astrophysics of Galaxies