Sexual maturation in triploid Pacific oysters (Crassostrea gigas) varies widely among individuals. In addition to genetic factors, the influence of the environment on their gonadal development is also crucial. To investigate the epigenetic regulation mechanism of Htatip2 DNA methylation in gonadal development in the Pacific oyster, the homology, phylogeny, gene expression and DNA methylation profiles at different developmental stages of fertile and sterile gonads in the oyster were investigated. The results showed that the conserved structural domain of Htatip2 in the Pacific oyster had the highest homology with the Htatip2-like conserved structural domain in the Eastern oyster (C. virginica). qPCR analysis showed that Htatip2 was expressed in various tissues, with the highest expression in the female gonads. In addition, the expression of Htatip2 increased with gonadal maturation in fertile oysters and did not change significantly in sterile oysters. BS-PCR analysis showed that the DNA methylation level of Htatip2 in oysters decreased with gonadal maturation and was negatively correlated with the gene’s expression level. Finally, the results of dual luciferase reporter assay indicated that the methylated Htatip2 promoter fragment significantly inhibited luciferase activity compared to the unmethylated fragment. This study suggests that DNA methylation of Htatip2 may be involved in the gonadal maturation through inhibition of gene expression. This study provides an important reference for the involvement of epigenetic regulatory mechanisms in gonadal development.