The DNA methyltransferase (DNMT) family primarily consists of DNMT1, DNMT3A, and DNMT3B, responsible for maintaining and establishing DNA methylation patterns crucial for epigenetic regulation. DNMT1 maintains methylation patterns during replication, while DNMT3A and DNMT3B are involved in de novo methylation of newly synthesized DNA. These enzymes are localized in the cell nucleus and regulate gene expression through methylation, influencing cell differentiation, development, and disease. They exhibit specificity in expression across different tissues and developmental stages, and mutations or dysregulation in their expression are associated with cancer, genetic diseases, and developmental abnormalities. Particularly, abnormalities in DNMT3A and DNMT3B are closely linked to the occurrence and progression of various malignant tumors.