  The changes of broad emission lines should be a crucial issue to
understanding the physical properties of changing-look active galactic nucleus
(CL-AGN). Here, we present the results of an intensive and homogeneous 6-month
long reverberation mapping (RM) monitoring campaign during a low-activity state
of the CL-AGN Seyfert galaxy NGC 3516. Photometric and spectroscopic monitoring
was carried out during 2018--2019 with the Lijiang 2.4 m telescope. The
sampling is 2 days in most nights, and the average sampling is $\sim$3 days.
The rest frame time lags of H$\alpha$ and H$\beta$ are
$\tau_{\rm{H}\alpha}=7.56^{+4.42}_{-2.10}$ days and
$\tau_{\rm{H}\beta}=7.50^{+2.05}_{-0.77}$ days, respectively. From a RMS
H$\beta$ line dispersion of $\sigma_{\rm{line}} = 1713.3 \pm 46.7$ $\rm{km}$
$\rm{s^{-1}}$ and a virial factor of $f_{\sigma}$ = 5.5, the central black hole
mass of NGC 3516 is estimated to be $M_{\rm{BH}}= 2.4^{+0.7}_{-0.3} \times
10^{7} M_{\odot}$, which is in agreement with previous estimates. The
velocity-resolved delays show that the time lags increase towards negative
velocity for both H$\alpha$ and H$\beta$. The velocity-resolved RM of H$\alpha$
is done for the first time. These RM results are consistent with other
observations before the spectral type change, indicating a basically constant
BLR structure during the changing-look process. The CL model of changes of
accretion rate seems to be favored by long-term H$\beta$ variability and RM
observations of NGC 3516.
