MUC1 is a highly glycosylated transmembrane mucin on the luminal surface of epithelial cells, protecting them from extreme factors. In cancer cells, MUC1 expression is upregulated and the protein structure, glycosylation level and spatial distribution are altered. It was found that upregulated MUC1 is involved in the regulation of several signaling pathways and plays an instrumental role in tumor cell metabolism, apoptosis, epithelial mesenchymal transition and distant metastasis. MUC1 glycosylation insufficiency leads to exposure of novel antigenic epitopes that can be used as specific targets for therapy and diagnosis. In addition, MUC1 was found to be closely related to HIF and can form a positive feedback loop leading to hypoxic malignant tumor progression. Currently, MUC1-based targeted drugs include monoclonal antibodies, antibody-coupled drugs, aptamers and cancer vaccines, some of which have already entered clinical trials. This paper reviews the role and mechanism of MUC1 in the biological function of malignant tumors and describes the potential of MUC1 in tumor-targeted chemotherapy, targeted radiotherapy and diagnostic imaging.