In order to study the mechanism of acoustic signal emission during laser drilling,acoustic and shock wave signal during laser drilling process were detected by microphone and PVDF sensor,the difference of acoustic signal was compared and analyzed when O2 was assisted gas and there was no assisted gas. Study results showed that the laser induced plasma shock wave when laser interact with materials is the main reason that generates the sound wave during percussion laser drilling process. Assist gas isn’t the necessary condition that generates sound wave. When assisted gas is O2,it can reduce the shielding effect of plasma and vapor on laser and maintain a continual output of sound wave;the oxidizing reaction between O2 and materials can enhance the shielding effect of plasma and vapor temporarily and lead to the discontinuous of the sound wave’s output.