Film micro-machining is a core in micro- and nano- technology, micro-electro-mechanical systems and photoelectron field. However, it is difficult to control the quality of machining in processing film. In the present paper the authors propose a method to solve this problem by using laser induced breakdown spectroscopy (LIBS). The authors investigated the relation between excitation condition and the quantity of plasma in the process of micro-machining by pulse laser. At low frequency (<20 Hz), when the excitation energy was confirmed, the quantity of plasma was steady and independent of the number of pulses. When the authors used single pulse to excite the film, the quantity of plasma increased with the energy ascension. Based on the quantity of plasma and the species of elements, the authors realized the real-time control of micro-machining become true.