Botulinum toxin type A (BTX-A) induces a reversible muscle paralysis at the injection site. There is evidence that BTX-A injection in specific facial muscles affects emotional experience and the processing of emotional stimuli (e.g., facial expressions, emotional language, and videos). Neuroscience research showed that BTX-A injection could attenuate amygdala activity, and could affect the neurocognitive function of reward system and other cerebral cortex as well. These findings can be interpreted by facial feedback hypothesis and social feedback hypothesis from the individual and social perspectives respectively. For subjects who received the injection, BTX-A reduces feedback from facial muscles thus impairing emotional experience and processing. According to this hypothesis, proprioceptive signals from facial muscles are conducted to the mesencephalic trigeminal nucleus and locus coeruleus, the latter of which sends direct projections to the thalamus, basal ganglia, and cerebral cortex related to motor, cognition, and emotion. In interpersonal communication, the observer’s emotional experience becomes similar to the subject who has received BTX-A injection through facial mimicry, and the subject’s emotional experience is also affected by the observer in turn. The mirror neuron system plays an important role in the process. Based on the existing researches, this review proposed an integrated model to explain the cognitive and neural mechanisms of how BTX-A injection affects emotional processing, which deepens the neural basis of facial feedback and social feedback for expression recognition and emotion processing. The model illustrates the roles of facial feedback and social feedback respectively as “signal resource” and “amplifier” of emotional processing caused by BTX-A injection, and the relationship between them. Specifically, the changes in muscles induced by facial mimicry causing emotional synchronization in social feedback process is in line with facial feedback process. The interaction of the two emotional processes could also cause multiple overlapping effects, which exist in both individual emotional processes and interpersonal interactions. Future studies should expand the aspects and levels of emotional processing, such as focusing on subliminal emotion processing and emotion regulation; further explore the mechanisms of how BTX-A injection affects emotional processing using neuroimaging technologies; improve the research paradigms to study the causal relationship between facial feedback and emotional processing; explore the mechanisms and application of BTX-A in the treatment of mental illness like depression; compare the effects of BTX-A injection and other invasive facial procedures on emotional processing. Further research will not only improve the understanding of cognitive and neural mechanisms underlying emotion but also have potential implications in mental health and medical cosmetology.