  Accurate determination of the stellar atmospheric parameters of RR Lyrae
stars (RRLs) requires short individual exposures of the spectra to mitigate
pulsation effects. We present improved template matching methods to determine
the stellar atmospheric parameters of RRLs from single-epoch spectra of LAMOST
(Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also known as the
Guoshoujing telescope). We determine the radial velocities and stellar
atmospheric parameters (effective temperature: $T_\mathrm{eff}$, surface
gravity: $\log{g}$, and metallicity: [M/H]) of 10,486 and 1,027 RRLs from
42,729 low-resolution spectra (LRS) and 7,064 medium-resolution spectra (MRS)
of LAMOST, respectively. Our results are in good agreement with the parameters
of other databases, where the external uncertainties of $T_\mathrm{eff}$,
$\log{g}$, and [M/H] for LRS/MRS are estimated to be 314/274 K, 0.42/0.29 dex,
and 0.39/0.31 dex, respectively. We conclude with the variation characteristics
of the radial velocities ($RV$) and stellar atmospheric parameters for RRLs
during the pulsation phase. There is a significant difference of $28\pm21$ km/s
between the peak-to-peak amplitude ($A_\mathrm{ptp}$) of $RV$ from H$\alpha$
line ($RV_\mathrm{H\alpha}$) and from metal lines ($RV_\mathrm{metal}$) for
RRab, whereas it is only $4\pm17$ km/s for RRc. The $A_\mathrm{ptp}$ of
$T_\mathrm{eff}$ is $930\pm456$ and $409\pm375$ K for RRab and RRc,
respectively. The $\log{g}$ of RRab show mild variation of approximately
$0.23\pm0.42$ dex near the phase of $\varphi = 0.9$, while that of RRc almost
remains constant. The [M/H] of RRab and RRc show a minor variation of about
$0.25\pm0.50$ and $0.28\pm0.55$ dex, respectively, near the phase of $\varphi =
0.9$.
