DNA methylation is specific, particularly in gene promoter regions, and can be used as cancer marker (15). In the present study, DNA methylation and mRNA expression **data** were retrieved from databases for T2DM and 13 types of cancer and bioinformatics analysis was used to identify key genes associated with differential gene expression and differential methylation. Gene interaction weighted networks were constructed and analyzed using the correlations of methylation levels of these genes, to understand the interactions between genes in an improved way. Ultimately, 8 genes were identified as co-morbid genes for T2DM and cancer. Since the information of different diseases is integrated in our network, the types of cancer involved in comorbid genes and their frequencies, as well as the connectivity values of gene nodes, all reflect the close relationship between T2DM and cancer. The results showed that among these 8 genes, the frequency of CRC was the highest (5/8). Therefore, it is considered that T2DM is more likely to be comorbid with CRC than the other 12 types of cancer, at least in terms of DNA methylation signatures.