In this work, the excimer-laser-induced crystallization of amorphous silicon (a-Si) films was investigated numerically and experimentally. This study had investigated the effects of irradiating energy density on the grain size and structure by scanning electron microscopy (SEM). In the surface microstructure analysis of the laser-irradiated area, the critical fluences (full-melt threshold, FMT) between the partial melting and complete melting regimes can be found by applying scanning electron microscopy. An efficient two-dimensional numerical model is carried out to predict the critical fluences (FMT) and the transient temperature distribution during the laser processing by the finite element method. An macro-micro model has been developed for the melting and resolidification of thin Si films induced by excimer-laser annealing. Except temperature distributions, the macro-micro models can offer more information about solidification process, such as undercooling, grain size, grain density etc. The algorithm that allows for nucleation is based on classical nucleation theory. Accordingly, the model enables the prediction of grain size, as well as the calculation of other critical responses of the a-Si film. The average grain sizes, obtained from the simulation results of the proposed model, agree fairly well with those from the experimental data.