This study investigated the expression pattern of the cyp19a gene during gonad development in grass carp (Ctenopharyngodon idellus) and the expression responses of various sex-related genes after RNA interference-mediated silencing of the target gene. The full-length cDNA sequence of the cyp19a gene was cloned using RACE technology, and the expression patterns of the cyp19a gene in gonadal tissues at different developmental stages of grass carp as well as in various tissues of adult fish were detected using qRT-PCR technology. Synthetic cyp19a-dsRNA was injected ino female grass carp for RNA interference experiments, while an equal volume of physiological saline was injected into the control group. The expression levels of sex-related genes in gonadal tissues and serum sex steroid hormone concentrations were then detected. The results showed that the full-length cDNA sequence of cyp19a in grass carp is 2219 bp, encoding an open reading frame of 1554 bp, a 5' UTR of 48 bp, a 3' UTR of 617 bp, and 517 amino acids encoded. The expression level of the cyp19a gene was highest in the gonads, followed by muscle, brain, and heart tissues. In gonads at different developmental stages, the expression level of cyp19a in ovaries was significantly higher than that in testes (P＜0.05) and significantly increases during the sexually mature stage at 48 months old, indicating that this gene plays a crucial role in the development and maturation of ovaries in grass carp. Five days after injection of 5 μg/g of cyp19a-dsRNA for silencing interference, the expression level of cyp19a in the dsRNA-injected group was significantly reduced compared to that in the control female fish (P＜0.05). The silencing efficiency of the target gene was 59.72% at 1 day post-injection and gradually increased thereafter. Compared to the control female fish, the dsRNA-injected group showed significant upregulation of foxl2a and foxl2b expression levels (P＜0.05) and downregulation of amh expression levels (P＜0.05) at 1 to 3 days post-injection, while dmrt1 expression levels were not significantly changed (P＞0.05). By 4 to 5 days post-interference, the expression levels of foxl2a, foxl2b, dmrt1, and amh in the dsRNA-injected group gradually returned to levels close to those of the control female group (P＞0.05). Furthermore, the serum estradiol (E2) levels in the injected group were significantly decreased (P＜0.05) compared to those in the control female fish, while testosterone (T) levels were significantly increased (P＜0.05). In conclusion, the expression level of the grass carp cyp19a gene, which belongs to the gonad aromatase gene, was highest in ovarian tissues, increased significantly during the sexual maturity stage, and may positively regulate foxl2a and foxl2b expression by negative feedback expression of dmrt 1 and amh. These results suggest that cyp19a plays a pivotal role in the development of ovaries and the nervous system in grass carp.