During the process of millisecond laser drilling of Ti6Al4V alloys, the recast layer forms along hole walls, which is a serious detriment to hole quality. In consideration of the thermal and mechanical parameters influencing melt and based on the modified equations of fluid mechanics and improved Level-Set method, a solid/liquid/gas three-phase two dimensional numerical model is constructed used for laser drilling. The numerical investigation of laser drilling with different pulse widths and with single pulse energy of 3 J is conducted. The temperature field, flow field, and thickness distribution of recast layer during the drilling process are obtained by using the post-processing technology. The results indicate that molten liquid is discharged mainly by means of evaporation and ejection and the recast layer is formed under the coupling effect of heat and force. The recast layer thickness increases with the increment of laser pulse width, which possesses a characteristic of recast layer becoming thin slowly from top hole to bottom hole.