Psoriasis can be treated with light therapy, and the use has increased in recent years, among which narrow-spectrum medium-wave ultraviolet therapy and 308nm single-frequency excimer laser therapy are more simple and practical with good efficacy compared with the previous photochemotherapy (PUVA is the treatment of psoriasis with internal psoralen-like drugs plus long-wave ultraviolet radiation). Narrow-spectrum medium-wave ultraviolet therapy is to treat psoriasis with narrow-spectrum medium-wave ultraviolet of 311nm wavelength. Its main mechanism is to affect cytokines and promote the synthesis of ossified triol, etc. At present, this kind of treatment is mainly used for psoriasis in clinical practice. It generally starts treatment with a minimum erythematous amount called the initial dose, 3 times a week, and can gradually increase the aforementioned dose by 10% according to the erythematous response. Most patients generally improve significantly with 8-9 treatments. Because no photosensitizing drugs are used, there are no adverse reactions of photosensitizers, and the operation is simple and convenient, with better safety. Narrow-spectrum medium-wave ultraviolet therapy can be combined with many drugs, such as the combined application of anthralin, carbofuran, Chinese medicine can make the therapeutic effect is enhanced, the current clinical has been widely used. However, the new method for the treatment of psoriasis that is currently emerging is the treatment of psoriasis with 308nm single frequency excimer laser. The mechanism of 308nm ultraviolet laser treatment for psoriasis is that it has a strong ability to induce T-cell apoptosis in psoriasis lesions, which is better than other therapies, and it is mainly used to treat psoriasis of common type, especially limited psoriasis lesions and psoriasis of hand and foot parts. In addition there is photodynamic therapy for psoriasis: this therapy is applied to the treatment of chronic plaque psoriasis in a small area. Patients with psoriasis use photosensitive substances and irradiate certain wavelengths of light to produce photochemical reactions to play a therapeutic effect outside, but very few people may have photosensitivity reactions.