It is now an indisputable fact that transurethral resection of non-muscle-infiltrating bladder tumors does not allow complete removal of the tumor, with a 33-76% incidence of residual tumors, usually located at the site of the resected tumor. Also, concurrent small tumors, especially flattened tumors, are not easily detected during the first surgery. Therefore, an important factor in the recurrence of bladder tumors is the inability to completely remove the primary tumor during transurethral resection of bladder tumors. Inability to completely remove the tumor can lead to recurrence within 12 months in 70% of bladder patients. Another factor is the inability of plain white light cystoscopy to detect bladder cancer in situ in a timely manner, leading to the risk of bladder tumor recurrence or progression. In addition, ordinary white light cystoscopy review encounters the illusion of tumor recurrence, resulting in radical cystectomy, when in fact there would have been no need for radical cystectomy. Finally, only after complete removal of the tumor, intravesical instillation of chemotherapy or immunotherapy is effective. Fu Weijun, Department of Urology, Beijing 301 Hospital, Beijing, China Blue light cystoscopy is the application of a photosensitizer (hexylaminolaevulinate, HAL) bladder perfusion followed by specific cystoscopy. Studies have reported a significant increase in the detection rate of carcinoma in situ and papillary tumors and a decrease in the recurrence rate of previously resected tumors. The principle of blue light cystoscopy is that photosensitizer bladder perfusion leads to selective accumulation of photoreceptors in rapidly growing cells (e.g., tumor cells), which fluoresce red against a blue background. Thus, the tumor lesion appears red against the normal blue bladder mucosa background. Compared to conventional plain white light cystoscopy, the application of blue light for photodynamic diagnosis of bladder cancer shows great advantages, with a statistically increased bladder tumor detection rate of 20-30%, a 25% reduction in residual tumor recurrence rate, and improved recurrence-free survival. Currently, the European panel recommends the following indications: 1. Improved bladder tumor detection rate, as well as tumor staging, in patients with early primary tumors who are suspected of having bladder cancer. To reduce and avoid random biopsies. 2, Patients with positive cytology, but negative white light examination. 4, Diagnosis and follow-up of patients with non-invasive (papillary uroepithelial tumors), invasive high-grade or in situ carcinoma, and multifocal tumors. 5.Application of flexible cystoscopy, which can be applied to outpatients with mucosal biopsy. 6.Teaching tools. Blue light cystoscopy can detect bladder tumor lesions that are not easily detected by ordinary white light cystoscopy.