  Grids of DAV star models are evolved by \texttt{WDEC}, taking the element
diffusion effect into account. The grid parameters are hydrogen mass
log($M_{H}/M_{*}$), helium mass log($M_{He}/M_{*}$), stellar mass $M_{\rm *}$,
and effective temperature $T_{\rm eff}$ for DAV stars. The core compositions
are from white dwarf models evolved by \texttt{MESA}. Therefore, those DAV star
models evolved by \texttt{WDEC} have historically viable core compositions.
Based on those DAV star models, we studied the rate of period change
($\dot{P}(k)$) for different values of H, He, $M_{\rm *}$, and $T_{\rm eff}$.
The results are consistent with previous work. Two DAV stars G117-B15A and R548
have been observed around forty years. The rates of period change of two
large-amplitude modes were obtained through O-C method. We did
asteroseismological study on the two DAV stars and then obtained a best-fitting
model for each star. Based on the two best-fitting models, the mode
identifications ($l$, $k$) of the observed modes for G117-B15A and R548 are
consistent with previous work. Both the observed modes and the observed
$\dot{P}$s can be fitted by calculated ones. The results indicate that our
method of evolving DAV star models is feasible.
