Graphite was ablated by a 400 us free-runing Nd:YAG laser and the reactivity photoacoustic spectra of ablation were detected . The acoustic spectra of ablation have a special double peak structure which does not depend on the length of the photoacoustic cell. The heavier the ablation is, the faster attenuation the ablating acoustic spectrum has. The rising time of the sound crest of ablation is about 400 us. With a 1. 10 mm diameter light spot on the surface of graphite, if the laser energy decreases from 3 ms to 8 ms, and the critical ablating energy of graphite is about 65 mJ. The peak value of the sound crest of ablation is directly proportional to laser energy. According to the analysis of the ablated spots by EMS, vaporization of graphite leads to double peaks in the acoustic spectrum and the corrugated surface on the inside surface of the ablated hole.