The structure of the nr4a1 gene in zebrafish （Danio rerio） was characterized with bioinformatics and a nr4a1^-/- zebrafish model was constructed with CRISPR-Cas9 genome editing to study in depth the mechanism of regulating the resistance to bacterial inflammation in fish. The expression dynamics of nr4a1， levels of inflammatory factors， bacterial clearance capacity， and histopathological changes in nr4a1^-/- zebrafish and a nr4a1-overexpressing ZF4 cell line following by the infection with Aeromonas hydrophila were systematically evaluated with quantitative real-time PCR （qPCR）， tissue bacterial load assessment， and pathological analysis to elucidate the role and mechanism of nr4a1 in A. hydrophila-induced hepatic inflammation in zebrafish. The results showed that the sequence of nr4a1 gene in zebrafish was highly conserved， with an open reading frame encoding a polypeptide of 574 amino acids. The predicted protein has an isoelectric point of 5.79 and a relative molecular mass of 63.04. The nr4a1 gene in zebrafish was widely expressed across various tissues. In nr4a1^-/- zebrafish， a 7 bp deletion in the second exon resulted in premature termination of translation， truncating the encoded protein from 574 aa to 297 aa. The relative expression of nr4a1 in liver tissues of zebrafish initially decreased and then increased after the infection with A. hydrophila. Compared with wild-type zebrafish， nr4a1^-/- mutants exhibited a lower survival rate， with a significantly higher bacterial loads and more severe hepatic pathological damage in liver tissues. The results of qPCR analysis showed that the expression level of inflammatory factors including il-1β， tnf-α， nf-κB and il-22v was significantly higher in nr4a1^-/- zebrafish than that in wild-type controls. On the contrast， overexpression of nr4a1 in ZF4 cells significantly inhibited the infection-induced upregulation of these inflammatory factors. It is indicated that Nr4a1 acts as a negative regulator to inhibit the expression of pro-inflammatory factors， thereby playing a crucial role in protecting the immune inflammatory response to A. hydrophila infection in zebrafish.