Photodynamic therapy (PDT) is a new technology that uses photodynamic response for disease diagnosis and treatment. In clinical practice, photodynamic therapy usually refers to photodynamic therapy only, while photodynamic diagnosis is called fluorescence diagnosis (Photodynamic Diagnosis, PDD). 1, the basic principle of photodynamic therapy The basic process of photodynamic reaction is the endogenous or exogenous photosensitive substances in biological tissues by the corresponding wavelength (visible light, near-infrared light or ultraviolet light) light irradiation, absorption of photon energy, from the ground state into the excited state, its physical degradation process can produce fluorescence, through the fluorescence spectral analysis can be diagnosed, and its chemical degradation process can produce a large number of Reactive oxygen, the most important of which is the single linear oxygen, reactive oxygen can interact with a variety of biological macromolecules, resulting in cytotoxic effects and cell damage or even death, thus producing therapeutic effects. In the field of dermatology, photodynamic therapy is used for the diagnosis of skin cancer or benign lesions with unclear boundaries and multiple occurrences, as well as for subclinical and latent infections that cannot be detected by the naked eye (such as subclinical condyloma acuminata and latent human papilloma virus infections). For example, in extramammary Paget’s disease and arsenic-induced Bowen’s disease, using PDD, fluorescent foci with many satellites can be found, and the fluorescence intensity decreases after photodynamic therapy, while the clinical manifestations or pathological manifestations are improved. 2.Photodynamic therapy (PDT) In the field of dermatology, PDT can be used to treat skin neoplastic diseases (e.g., basal cell epithelioma, Bowen’s disease, squamous carcinoma, extramammary Paget’s disease, actinic keratosis and proliferative erythema, etc.); it can also be used to treat skin non-neoplastic diseases (e.g., condyloma acuminata, acne, flat warts and toe warts, etc.). Since the introduction of photodynamic therapy in 2007, our department has successfully treated a variety of skin cancers (such as basal cell epithelioma, Bowen’s disease, squamous carcinoma, extramammary Paget’s disease, etc.) and achieved satisfactory results. Among the non-neoplastic skin diseases, domestic multi-center clinical trials have shown that photodynamic therapy for acromegaly (CA), especially for male urethral warts, is simple, effective, well tolerated, and has the advantages . It is effective for subclinical infection and latent infection with low recurrence rate. It has a good application prospect. Our department has also treated more than 300 cases of condyloma acuminata since the photodynamic therapy was carried out in November last year, including male urethral and other parts of the genital warts, rectal condyloma acuminata, perianal condyloma acuminata, female cervical and vulvar condyloma acuminata, most of the patients achieved satisfactory results after 2 to 4 times of photodynamic therapy treatment. Recently, for the treatment of condyloma acuminata, domestic has concluded 3 stages of treatment to remove papilloma virus infection program, to reduce condyloma acuminata recurrence has a very good effect. 3, the prospect of photodynamic therapy photodynamic therapy has been introduced for more than twenty years, with its unique advantages show a strong vitality. As a new treatment method, photodynamic therapy has the following characteristics: highly selective for cancer cells and other highly proliferative cells; does not affect other treatments and have a synergistic effect, can repeat treatment; less toxic side effects, relatively safe; short treatment time, fast onset of action; has a good cosmetic effect. Many scholars at home and abroad have been devoted to research in this area. We believe that with the emergence of new photosensitizers, the improvement of lasers and the further development of basic and clinical research on PDT, PDT will become a good diagnostic and therapeutic tool with broad application prospects.