The lytic polysaccharide monooxygenase (LPMO) of AA9 is widely distributed in fungi and plays an important role in the bioconversion of biomass because it can degrade crystalline polysaccharide of lignocellulose. The detailed information of the structural features, catalytic mechanism, structure and function and microbial expression and regulation of AA9 LPMO is summarized. Finally, the applications of AA9 LPMO in the conversion of lignocellulose are also discussed.