Stress-induced neuroepigenetic programming gains growing more and more interest in the studies of the etiology of posttraumatic stress disorder (PTSD). However, seldom attention is focused on DNA demethylation in fear memory generalization, which is the core characteristic of PTSD. Here, we show that ten-eleven translocation protein 3 (TET3), the most abundant DNA demethylation enzyme of the TET family in neurons, senses environmental stress and bridges neuroplasticity with behavioral adaptation during fear generalization. Foot shock strength dependently induces fear generalization and TET3 expression in nucleus accumbens (NAc) in mice. Inhibition of DNA demethylation by infusing demethyltransferase inhibitors or AAV-Tet3-shRNA virus in NAc enhances the fear generalization and anxiety-like behavior. Furthermore, TET3 knockdown impairs the dendritic spine density, PSD length, and thickness of neurons, decreases DNA hydroxymethylation (5hmC), reduces the expression of synaptic plasticity-related genes including Homer1, Cdkn1a, Cdh8, Vamp8, Reln, Bdnf, while surprisingly increases immune-related genes Stat1, B2m, H2-Q7, H2-M2, C3, Cd68 shown by RNA-seq. Notably, knockdown of TET3 in NAc activates microglia and CD39-P2Y12R signaling pathway, and inhibition of CD39 reverses the effects of TET3 knockdown on the fear memory generalization and anxiety. Overexpression of TET3 by Crispr-dSaCas9 virus delivery to activate endogenous Tet3 in NAc increases dendritic spine density of neurons in NAc and reverses fear memory generalization and anxiety-like behavior in mice. These results suggest that TET3 modulates fear generalization and anxiety via regulating synaptic plasticity and CD39 signaling pathway.