As a kind of intraoperative navigation technology, near infrared fluorescence imaging has become more and more important in the biomedical field. Its non-invasive, high sensitivity and high resolution characteristics make it a useful assistant in biomedical research. Although traditional biooptical imaging techniques such as IR-I can provide rich physiological and pathological information, they still have limitations in some aspects, such as high cost, complex operation and low detection efficiency. Therefore, a more advanced, efficient and convenient imaging technology is urgently needed to meet the needs. It is in this context that the fluorescence imaging technology of IR-II came into being. Because of its unique tissue penetration depth and low background noise, near infrared two region (NILII) fluorescence imaging technology has shown great potential and broad application prospects in the field of biomedical imaging. Based on this, the background principle of NIL-II fluorescence imaging technology and the challenges facing the development of NIL-II fluorescence probes will be presented, and the application of indocyanine green (ICG) as a NIL-II fluorescence probe in the medical field will be introduced, and the practical application of NIL-II fluorescence imaging in tumor diagnosis and treatment will be introduced.