Since the invention of lasers in the 1960s, the pulse duration has being continuously shorten down to the sub-picosecond and even femtosecond regime. It makes the laser processing technology to the ultrashort pulse laser era. In order to further optimize the ultrashort pulse laser micro-machining, theoretical study is indispensable. The interaction mechanism between ultrashort pulse laser and different types of materials were presented. The typical physical properties, such as plasma effect, self-focusing and filamentation, and conical radiation, were discussed. The theoretical studies for ultrashort pulse laser drilling of micro-hole were analyzed. Furthermore, the challenging issues were obtained.