Background: N1-methyladenosine (m1A) is a recently identified mRNA modification. It is still unclear, though, whether m1A alteration affects how colorectal cancer (CRC) develops. Methods: We retrospectively analyzed 398 CRC patients and 39 normal controls using the TCGA database to evaluate m1A modification patterns regarding tumor immune microenvironment (TIME) in CRC. The m1Ascore was developed using principal component analysis. And its clinical value in prognosis of CRC was further explored. Results: We revealed 12 key m1A-related DEGs including CLDN3, MUC2 and CCDC85B which are identified associated with invasion and metastasis in CRC. The most important biological processes linked to a weak immune response and a poor prognosis were the regulation of RNA metabolism and RNA biosynthesis. Furthermore, we found that compared to CRC patients with low m1A scores, those with high m1A scores had a higher percentage, a larger tumor burden, and a worse prognosis for survival. Conclusion: Significantly diverse m1A modification patterns can be seen in CRC. Through its impact on TIME and immunological dysfunction, the heterogeneity of m1A alteration patterns influences the prognosis of CRC. This study provided novel insights into the m1A modification in CRC which might promote the development of personalized immunotherapy strategies.