DNA methylation, one of the best-characterized epigenetic modifications, plays essential roles in diseases, including human cancers. In recent years, our understanding on DNA methylation with human cancers has made significant progress, which was facilitated by stunning development in the analysis of the human methylome of multiple cancer types. In this review, recent developments in the characterization of aberrant DNA methylation involved in human cancers development were discussed with special emphasis on the mechanisms of aberrant DNA methylation in human cancers. We also summarize the recent treatment strategy for human cancers with de-methylation drugs.