Recently, ultra-short pulsed lasers with high peak power have been developed, and their application to the materials processing is expected for a tool of precision microfabrication. During surface generation process with laser ablation, lattice defects such as dislocations, vacancies, grain boundaries, are also generated beneath the surface. Lattice defects influence the quality or accuracy of materials processing, therefore it is important for laser precision microfabrication to elucidate the generation mechanism of them. In this paper, laser ablation phenomena of metal were analyzed using the modified molecular dynamics method, which has been developed by Ohmura and Fukumoto. Main results obtained are summarized as follows: (1) The shock wave induced by the Gaussian beam irradiation propagates radially from the surface to the interior. (2) A lot of dislocations are generated near the surface by the propagation of shock wave. (3) Many grains are generated in the resolidification process after the end of laser pulse. They are metastable and some crystal-orientations of them change to one of the base metal and the grain boundaries disappear in the cooling process.