Colorectal cancer originates from the epithelium of the large intestine and is a common malignant tumor in the gastrointestinal tract. However, the relationship between RRP9 and DDX21 and colorectal cancer (CRC) remains unclear. GSE134834, GSE206800, and GSE209892 profiles for CRC were downloaded from the gene expression omnibus database generated using GPL20115 and GPL23126. Differentially expressed genes (DEGs) were screened and weighted gene co-expression network analysis was performed. The construction and analysis of protein-protein interaction network. Functional enrichment analysis and gene set enrichment analysis were performed. Gene expression heat map was drawn and immune infiltration analysis was performed. Comparative toxicogenomics database analysis were performed to find the disease most related to the core gene. TargetScan was used to screen miRNAs regulating central DEGs. One thousand three hundred eighty DEGs were identified. According to gene ontology analysis, they were mainly concentrated in signal receptor activity regulation and metal titanase activity. Kyoto encyclopedia of gene and genome analysis showed that they mainly focused on IL17 signal pathway, PPAR signal pathway, protein digestion, and absorption, and the interaction of viral proteins with cytokines and cytokine receptors. The intersection of enrichment items and GOKEGG enrichment items of differentially expressed genes is mainly concentrated in PPAR signal pathway and the interaction of viral proteins with cytokines and cytokine receptors. The protein-protein interaction network obtained 16 core genes (MAD2L1, MELK, TPX2, UBE2C, RFC4, PLK1, RACGAP1, DKC1, DDX21, L Y AR, WDR3, RRP9, WDR43, NOLC1, BRIX1, and GTPBP4). Heat map of gene expression showed that core genes (TPX2, UBE2C, RFC4, PLK1, DKC1, LYAR, WDR3, NOLC1, and BRIX1) were not significantly differentially expressed between CRC and normal tissue samples. Core genes (MAD2L1, MELK, RACGAP1, RRP9, WDR43, DDX21, and GTPBP4) were highly expressed in CRC tissue samples and lowly expressed in normal tissue samples. Comparative toxicogenomics database analysis showed that 7 genes (MAD2L1, MELK, RACGAP1, RRP9, WDR43, DDX21, and GTPBP4) were related to necrosis, inflammation, tumor, precancerous symptoms, hemorrhage, and weightlessness. RRP9 and DDX21 are highly expressed in CRC. The higher the expression level of RRP9 and DDX21, the worse the prognosis.