The characteristics, mechanisms, and maximum possible magnitude of injection- induced earthquakes are important to study for induced earthquake prevention, risk assessment, and disaster reduction strategy formulation. This paper systematically collates the main understandings and disputes of injection- induced earthquake research at home and abroad. The results indicate that the maximum possible magnitude of an induced earthquake, which is affected by water injection parameters such as injection pressure and cumulative injection volume, is determined by geological conditions such as fault size and stress state. The reliable method for identifying induced earthquakes depends on a series of evidence chains, including the time- space correlation between earthquakes and water injection, the parameters of the statistical model, and the analysis of fault activation. When a hydraulic connection exists between the fault and the fluid reservoir, the pore pressure disturbance is the main induction mechanism; when the fluid pathway is unavailable, the change in pore elastic stress caused by the volume deformation of the rock matrix plays a dominant role. In addition, the chemical action of fluid and the triggering effect of small earthquakes may also play an important role in injection- induced earthquakes. This study provides a scientific reference for studying the mechanism of injection- induced earthquakes and the mitigation of destructive induced earthquake disasters.