The SET domain group (SDG) gene family controls histone lysine methylation, which is an important part of the regulation of chromatin function and epigenetic regulation of gene expression. To understand the biological function of longan (DlSDG) family, the whole SDG family members of longan genome were identified by bioinformatics analysis, and the protein domain, conserved motif, gene structure, promoter homeopathic elements, evolutionary tree, protein interaction of related genes and gene expression at the early stage of somatic embryogenesis were predicted and analyzed. There were 32 members of longan DlSDG gene family, which could be divided into seven subfamilies, Suv, Ash, ATXR5/ATXR6, Trx, E(z), SMYD and SETD, and Suv had the largest subfamily members. The number of exons varied from 1 to 22, and protein domains were conserved, all containing a SET domain. DlSDG protein conserved motif had large differences among different subfamilies. DlSDG promoters contained many abiotic stress response elements such as low temperature, drought, stress and hormone response elements. SDG members could be expressed to different degrees in the early stage of somatic embryogenesis. DlSUVR4b might play an important role in EC and ICpEC stages. DlSUVH4 could interact with DNA methyltransferase MET1. The study showed that the longan DlSDG 32 histone lysine methylation transferase genes maight directly involved in the regulation of stress response and somatic embryogenesis, possibly in DNA methylation, chromatin remodeling, formation in the process of somatic embryogenesis of collaborative control network in addition to the regulation of the circadian clock, branch number, root growth and development, seed germination, the growth of flowers and plants of morphogenesis with diversity and complexity.