B7-H3 is one of the most important members of the B7/CD28 family, and its expression level is abnormally high in a variety of tumors. B7-H3 inhibits T cell activation via binding to the corresponding receptors on T cells, thereby mediating tumor immune escape. Glycosylation is a common post-translational modification of proteins, which plays an essential role in protein expression patterns and biological functions. Current evidence has shown that the abnormal glycosylation of B7-H3 in tumors is of great significance for protein expression and ligand-receptor binding. Therefore, in-depth exploration of the underlying mechanism of glycosylation modification of B7-H3 is expected to provide new insights for tumor immunotherapy. To investigate the underlying mechanism of glycosyltransferase-mediated glycosylation of B7-H3. Firstly, the CHIPBase database was used to screen glycosyltransferases with a high correlation with the protein expression of B7-H3. Then their siRNAs were designed and synthesized to transfect into cells, and the western blotting assay was performed for further screening. Secondly, the siRNA and overexpression plasmid of the screened glycosyltransferase were respectively transfected into cells to verify the effect on the expression level of B7-H3. Thirdly, the effect of glycosyltransferase on the expression level of B7-H3 was explored by changing its substrate level. Finally, the co-immunoprecipitation experiment was conducted to verify whether protein binding existed between B7-H3 and the glycosyltransferase. The glycosyltransferase called A4GALT had the highest correlation with the protein expression of B7-H3. After knocking down or overexpressing A4GALT, the protein expression level of B7-H3 both changed significantly. When knocked down GALT to reduce the galactosyl donors, B7-H3 was significantly down-regulated. And B7-H3 was up-regulated while increasing the galactose in the medium. In addition, the Co-immunoprecipitation experiment proved that there was protein binding between B7-H3 and A4GALT. A4GALT can positively regulate the expression of B7-H3, and changing the level of galactosyl donors can also positively regulate the expression of B7-H3. There is a protein interaction between A4GALT and B7-H3.