To explore the mechanism of the long-pulse laser interaction with semiconductor materials, a one-dimensional finite element calculational model was established to investigate the vaporization effect of the long-pulse laser interaction with the silicon. In the calculation, Enthalpy method was used to resolve the process of solid-liquid phase change, and the heat flux equation was used to analyze the energy loss of vaporization. With the certain incident laser power density and different pulse widths,the long pulse laser interaction with the silicon in the process of melting and vaporization phenomena was simulated. The vaporization velocity, temperature evolvement, and the effect of vaporization on ablation depth during and after the laser irradiation were emphatically analyzed. Furthermore, the atomic vapor induced self-focusing threshold by laser transmission was estimated to be about 0.2 W when vaporization depth was about 0.5 μm,which was far less than the long-pulse laser power. Therefore, the follow-up laser will cause optical self-focusing phenomenon by vaporization in the long pulse laser interaction with the silicon, obtained results can provide the theoretical basis for the research on the mechanism of the laser interaction with the silicon.