Objective To analyze the differentially expressed genes between colorectal cancer tissues and normal tissues based on The Cancer Genome Atlas (TCGA) and to explore the related molecular mechanisms.Methods We downloaded all mRNA transcriptome data about colorectal cancer from the TCGA database, and obtained data on a total of 740 cases, including 571 cases of colorectal cancer tissues and 169 cases of normal tissues. The edgeR package in R was used to process the data and to screen differentially expressed genes. The DAVID database was applied to perform the enrichment analysis of Gene Ontology (GO) terms and KEGG pathways on the top 1,000 differentially expressed genes. The top 200 differentially expressed genes were used to establish the protein-protein interaction network based on the Cytoscape software. The expression of hub genes in cancer tissues and normal tissues was compared. The cases were then divided into high expression group and low expression group according to the expression of the hub genes, with the median expression levels of these genes as the cut-off values. The survival between the high expression group and low expression group was compared.Results A total of 5,073 differentially expressed genes were screened, including 2,136 up-regulated genes and 2,937 down-regulated genes. GO analysis showed that the biological processes were mainly enriched in cell proliferation, transport, rRNA processing, and receptor-mediated endocytosis. KEGG enrichment analysis showed that the signaling pathways of differentially expressed genes were mainly associated with cell cycle, transcriptional misregulation in cancer, bile secretion, thyroid hormone signaling pathway, and platelet activation. The top seven hub genes were PLK1, BRD4, EHMT2, HIST2H4B, PRPF19, SUV39H1, and TRIM28. A further verification exhibited that the expression of PLK1, PRPF19, and SUV39H1 in colorectal cancer tissues was higher than that in normal tissues (P < 0.05). According to the survival analysis, there was no significant difference in the overall survival between the groups with the high expression and the low expression of PLK1 and SUV39H1 (P > 0.05), while the overall survival was greater in the group with the low expression of HIST2H4B than that in the group with the high expression of HIST2H4B (P < 0.05).Conclusions Based on the TCGA database, PLK1 is highly expressed in colorectal cancer tissues. It is involved in cell proliferation, G2/M transition of the mitotic cell cycle, and other biological processes. Through the P53 signaling pathway, PLK1 plays a role in the development and progression of colorectal cancer and is expected to be a tumor marker for the diagnosis of colorectal cancer.