The purpose of this study is to investigate the regulatory role of dnmt3a in the sex reversal process of Chinese tongue sole， and to develop a DNA methylation editing system suitable for Chinese tongue sole. In this study， we cloned the CDS region of dnmt3a of Chinese tongue sole and analyzed structural domain features and sequence conservation between different species. We analyzed the expression pattern of dnmt3a in male， female and pseudomale Chinese tongue sole by qPCR. We also investigated the effect of a DNA methylase inhibitor 5-Aza-dC treatment on dnmt3a gene expression. The results showed that the full-length cDNA of dnmt3a was 3 063 bp， encoding 1 020 amino acids， including three core domains （PWWP domain， ADDz domain and AdoMet_MTases superfamily）. The bound structural domain （PWWP domain， ADDz domain） of dnmt3a was relatively conservative， but the catalytically active domains （AdoMet_MTases superfamily） were quite different from those of mammals and reptiles. Gene expression pattern analysis showed that the expression of dnmt3a was significantly higher in female gonads than in male and pseudo-male gonads. The relative expression of dnmt3a increased significantly after 5-Aza-dC treatment. This study indicates that dnmt3a plays an important role in the sex regulation of Chinese tongue sole by DNA methylation， which provides a reference for elucidating the sex reversal mechanism and the implementing of DNA methylation editing to target single gene in Chinese tongue sole.