Grids of DAV star models are evolved by 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* and effective temperature T-eff for DAV stars. The core compositions are from white dwarf models evolved by MESA. Therefore, DAV star models evolved by WDEC have historically viable core compositions. Based on those DAV star models, we studied the rate of period change ((P) over dot(k)) for different values of H, He, M* and T-eff. The results are consistent with previous work. Two DAV stars G117-B15A and R548 have been observed for around 40 years. The rates of period change of two large-amplitude modes were obtained through the O - C method. We conducted an 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. (P) over dots(s) can be fitted by calculated ones. The results indicate that our method of evolving DAV star models is feasible.