  NGC 5548 is one of the active galactic nuclei (AGN) selected for our
long-term spectroscopic monitoring with the Lijiang 2.4~m telescope, aiming at
investigating the origin and evolution of the broad-line regions (BLRs),
accurately measuring the mass of the supermassive black holes (SMBHs), and
understanding structure and evolution of the AGN. We have performed five-season
observations for NGC~5548 with the median sampling interval ranging from 1.25
to 3 days. The light curves of the 5100~\AA\ continuum and broad emission lines
are measured after subtracting contamination of the host galaxy starlight. The
time lags of the broad He~{\sc ii}, He~{\sc i}, H$\gamma$, and H$\beta$ lines
with respect to the 5100~\AA\ continuum are obtained for each season and their
mean time lags over the five seasons are 0.69, 4.66, 4.60, 8.43 days,
respectively. The H$\gamma$ and H$\beta$ velocity-resolved lag profiles in the
seasons of 2015, 2018, 2019, and 2021 are constructed, from which an
``M-shaped'' structure is found in 2015 but disappears after 2018. Our
five-season reverberation mapping (RM) yields an averaged virial SMBH mass of
$M_\bullet/10^7M_\odot=14.22$, with a small standard deviation of $1.89$. By
combining the previous 18 RM campaigns and our five-season campaign for
NGC~5548, we find that there exists a time lag of 3.5~years between the changes
in the BLR size and optical luminosity. In addition, we also construct the BLR
radius$-$luminosity relation and the virial relation for NGC~5548.
