  The Sandage-Loeb (SL) test is a promising method for probing dark energy
because it measures the redshift drift in the spectra of Lyman-$\alpha$ forest
of distant quasars, covering the "redshift desert" of $2\lesssim z\lesssim5$,
which is not covered by existing cosmological observations. Therefore, it could
provide an important supplement to current cosmological observations. In this
paper, we explore the impact of SL test on the precision of cosmological
constraints for two typical holographic dark energy models, i.e., the original
holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE)
model. To avoid data inconsistency, we use the best-fit models based on current
combined observational data as the fiducial models to simulate 30 mock SL test
data. The results show that SL test can effectively break the existing strong
degeneracy between the present-day matter density $\Omega_{m0}$ and the Hubble
constant $H_0$ in other cosmological observations. For the considered two
typical dark energy models, not only can a 30-year observation of SL test
improve the constraint precision of $\Omega_{m0}$ and $h$ dramatically, but can
also enhance the constraint precision of the model parameters $c$ and $\alpha$
significantly.
