  Expected to be of the highest survey power telescope in the northern
hemisphere, the Wide Field Survey Telescope (WFST) will begin its routine
observations of the northern sky since 2023. WFST will produce a lot of
scientific data to support the researches of time-domain astronomy, asteroids
and the solar system, galaxy formation and cosmology and so on. We estimated
that the 5 $\sigma$ limiting magnitudes of WFST with 30 second exposure are
$u=22.31$ mag, $g=23.42$ mag, $r=22.95$ mag, $i=22.43$ mag, $z=21.50$ mag,
$w=23.61$ mag. The above values are calculated for the conditions of
$airmass=1.2$, seeing = 0.75 arcsec, precipitable water vapour (PWV) = 2.5 mm
and Moon-object separation = $45^{\circ}$ at the darkest New Moon night of the
Lenghu site (V=22.30 mag, Moon phase $\theta=0^{\circ}$). The limiting
magnitudes in different Moon phase conditions are also calculated. The
calculations are based on the empirical transmittance data of WFST optics, the
vendor provided CCD quantum efficiency, the atmospherical model transmittance
and spectrum of the site. In the absence of measurement data such as sky
transmittance and spectrum, we use model data.
