Background and Study Aims: To observe the efficacy of photodynamic therapy in patients with advanced gastric cancer and analyze the reasons affecting the efficacy. Methods: In this paper, a patient with advanced gastric cancer in our hospital was selected.HoPorfin is used as a photosensitizer and photodynamic therapy was performed 48 hours and 72 hours later. Results: One month after the photodynamic treatment, the patient came to our hospital to reexamine the gastroscope. Through the comparison of gastroscopy before and after the photodynamic treatment, the gastric cancer lesion of the patient after the photodynamic treatment was not significantly smaller than before, and the effect of photodynamic treatment was not ideal. Conclusion: The four reasons for the unsatisfactory effect: individual differences of patients, photosensitizer, light source and oxygen.