Objective: To investigate the potential value of PDT(photodynamic therapy) in the treatment of rectal cancer by reviewing the diagnosis and treatment process of a patient with advanced rectal cancer who lost the opportunity of surgery. Methods: Select the case data of a patient receiving photodynamic therapy in our hospital, and analyze the photodynamic mechanism, safety and efficiency, and discuss the efficacy of photodynamic therapy. Results: After the patient received photodynamic therapy, re-examination of the endoscopy showed that the intestinal cavity was smoother than before, the bowel was difficult, and the symptoms of blood in the stool improved. Conclusion: Photodynamic therapy can be used as a radical or palliative treatment for clinical tumor treatment. Because of its advantages of minimally invasive, tissue-specific, repetitive and synergistic radiotherapy and chemotherapy, it plays an important role in early or middle-advanced colorectal cancer and is worthy of clinical promotion.