Neutrophils play their roles via phagocytosis, degranulation and producing reactive oxygen species(ROS). Moreover, a new reaction mechanism of neutrophils producing neutrophil extracellular traps (NETs) has been reported. NETs take part in the innate immune responses. The formation of NETs is called NETosis, which belongs to programmed cell death. NETs could be formed in response to neutrophils activation by a series of processes, including ROS production, neutrophil elastase (NE) and myeloperoxidase (MPO) transportation to nucleus, histones modification, chromatin decoagulation, and membrane breakage. This process is called NADPH-dependent NETosis. In addition, peptidyl arginine deiminase 4 (PAD4) is needed for NADPH-independent NETosis. Furthermore, NETs can also be rapidly formed. Herein, we mainly reviewed the mechanism of NETosis.