Trimethylated histone H3 at lysine 27（H3K27me3）is one of the most common histone methylation modifications and is produced by polycomb repressive complex 2，while changes in the components of polycomb repressive complex 2，such as altered function or overexpression of enhancer of zeste homolog-2 will show an imbalance in H3K27me3 expression，resulting in uncontrolled cell proliferation and differentiation and leading to tumorigenesis. Loss of histone modification of H3K27me3 has been found in a variety of tumors，for example，breast，ovarian，and pancreatic cancers. However，there is heterogeneity in the expression and prognosis of H3K27me3 in different tumors. In this paper，the expression and biological function of H3K27me3 in different tumors and its value in the diagnosis，treatment and prognosis of tumors were summarized and investigated，providing new ideas for the study of tumors.