Sex steroid hormones are closely related to biological reproduction, gamete emission and gonadal development. And Srd5a1 plays an important role in the synthesis of sex steroid hormones. In order to investigate the effect of the sex steroid hormone synthesis-related enzyme gene Srd5a1 on ovarian development in female Hyriopsis cumingii, Srd5a1 was obtained from the gonads of H.cumingii by RACE (Rapid-amplificiantion of cDNA ends). The expression characteristics of Srd5a1 were investigated by real-time fluorescence quantification (qRT-PCR), in situ hybridization and in vitro induction of 17β-estradiol (E2) and 17α-methyltestosterone (MT) at different concentrations for 24 days. The results showed that the full-length cDNA of Srd5a1 was 2 224 bp, including ORF 825 bp, 3'-UTR 953 bp, and 5'-UTR 446 bp, encoding 274 amino acids. The expression of Srd5a1 in the gonad was bimodal, with higher expression in the ovary than that in the testis; Srd5a1 had the highest expression level in the ovarian discharge period, which was extremely significantly higher than that in all other periods. In situ hybridization results showed that Srd5a1 detected positive signals in ovarian oocytes and follicles as well as spermatocytes of the testis. The expression of Srd5a1 was changed after 24 days of treatment with different concentrations of E2 and MT. In conclusion, Srd5a1 may play a role in the developmental maturation of the ovary oocyte and gamete emission in the female H. cumingii. This study is important for exploring the gonadal growth and development of H. cumingii, and also provides a theoretical reference value for the realization of monogamous breeding of H. cumingii.