An experimental study on the process of backside wet etching sapphire induced by pulse fiber laser is carried out by acoustic emission detector. In the backside wet etching sapphire process induced by laser, the detected acoustic emission signal contains a lot of characteristic information. The backside wet etching sapphire process can be characterized by parameters such as amplitude, marse and hit-counting of acoustic emission signal. Before the sapphire is cut through, the acoustic emission signal shows few acoustic emission events, large amplitude of 90-100 dB, large marse and small hit-counting. After the sapphire is cut through, the acoustic emission signal shows many acoustic emission events, small amplitude of 40-80 dB. Meanwhile, the marse becomes nearly zero, and the hit-counting is large.