  The Tsinghua University-Ma Huateng Telescope for Survey (TMTS) has been
constantly monitoring the northern sky since 2020 in search of rapidly variable
stars. To find variable white dwarfs (WDs), the TMTS catalog is cross-matched
with the WD catalog of Gaia EDR3, resulting in over 3000 light curves of WD
candidates. The WD TMTS J17184064+2524314 (hereafter J1718) is the second
ZZ~Ceti star discovered among these common sources. Based on the light curves
from TMTS, follow-up photometric observations, and TESS, 10 periods and 3
combination periods are detected. A rotation period of $25.12\pm0.18$ hr is
derived, according to the identified rotational splitting. Our spectroscopic
observation indicates that this WD belongs to DA type with $T_{\rm
eff}=11,670\pm604$ K, log $g=8.16\pm0.36$, $M = 0.70\pm0.23$ M$_{\odot}$, and
age=$0.51\pm0.34$ Gyr. Based on core-parameterized asteroseismological model
grids ($\geqslant$ 14 million), we derive a best-fit solution of $T_{\rm
eff}=11,640\pm20$ K, log $g=8.267\pm0.008$, and $M = 0.750\pm0.005$ M$_{\odot}$
for J1718, consistent with the spectral fitting results. For this WD, the
corresponding carbon and oxygen abundances in the core are 0.43 and 0.57,
respectively. The distance derived from the intrinsic luminosity given by
asteroseismology is $64\pm15$ pc, in accord with the distance of $70.1\pm0.2$
pc from Gaia DR3 within the uncertainties.
