Fear generalization is a phenomenon that conditioned fear responses extended to safe stimuli which shares perceptual similarity with threat stimuli. Moderate fear generalization is beneficial for human survival, but excessive fear generalization leads to maladaptation to environment. Rules that underlie fear generalization have been investigated by related researches based on perception, and been widely applied to studies in various domains. This paper reviews the study of the generalization of fear based on perception. Here, we begin with Pavlovian fear conditioning and the gradient of fear generalization, which lays the foundation for theoretical approaches used today. Then we review the research of fear generalization based on perception in multiple sensory channels (i.e., visual, auditory, context). Third, we summarize the neural circuits of fear generalization which involve hippocampus, amygdala, insula, and prefrontal cortex. Last but not least, we briefly clarify the difference between perception-based and concept-based fear generalization which receive increased interests. Further studies should extend this work in many ways, such as combining concepts-based fear generalization, using Just-Noticeable-Difference Threshold to ensure that the generalization stimuli can actually be discriminated, increasing the explicitness and divisity of stimuli, as well as applping hormonesand multi-modal data analysis methods.