  The Chinese Space Station Telescope (CSST) spectroscopic survey aims to
deliver high-quality low-resolution ($R > 200$) slitless spectra for hundreds
of millions of targets down to a limiting magnitude of about 21 mag,
distributed within a large survey area (17500 deg$^2$) and covering a wide
wavelength range (255-1000 nm by 3 bands GU, GV, and GI). As slitless
spectroscopy precludes the usage of wavelength calibration lamps, wavelength
calibration is one of the most challenging issues in the reduction of slitless
spectra, yet it plays a key role in measuring precise radial velocities of
stars and redshifts of galaxies. In this work, we propose a star-based method
that can monitor and correct for possible errors in the CSST wavelength
calibration using normal scientific observations, taking advantage of the facts
that i) there are about ten million stars with reliable radial velocities now
available thanks to spectroscopic surveys like LAMOST, ii) the large field of
view of CSST enables efficient observations of such stars in a short period of
time, and iii) radial velocities of such stars can be reliably measured using
only a narrow segment of CSST spectra. We demonstrate that it is possible to
achieve a wavelength calibration precision of a few
$\mathrm{km}\,\mathrm{s}^{-1}$ for the GU band, and about 10 to 20
$\mathrm{km}\,\mathrm{s}^{-1}$ for the GV and GI bands, with only a few hundred
velocity standard stars. Implementations of the method to other surveys are
also discussed.
