1, long-wave ultraviolet (UVA): wavelength of 320-400 nm, the application of UVA irradiation treatment alone will produce mild to moderate improvement, not recommended at the same time for other forms of phototherapy, UVA treatment is most commonly used as part of PUVA therapy. 2, photochemotherapy (PUVA): photochemotherapy is a combination of oral or topical psoralen (8-MOP, 5 a MOP) and UVA, a few can also apply UVB (290-320 rim) method. It is mainly used for the treatment of moderate and severe psoriasis. It includes generalized common psoriasis, limited plaque psoriasis (topical psoralen + UVA) erythrodermic psoriasis and pustular psoriasis. Oral psoralen can cause gastrointestinal symptoms, such as nausea; high UVA exposure can cause skin erythema, burning, blistering, etc. Long-term application of PUVA can cause skin aging, pigmentation and skin cancer; there is an increased risk of cataract. 3. Broad-spectrum UVB: Medium-wave UVB with a wavelength of 290-320 nm. It is often used in the treatment of moderate and severe psoriasis, or local stubborn plaques. However, it can cause erythema, sunburn and hyperpigmentation. Long-term exposure has the potential to cause cancer. Broad-spectrum UVB can be used in combination with internal and/or external drugs to increase the efficacy. 4.Narrow-spectrum UVB: Medium-wave UVB with wavelength (308, 310, 311, 312nm). It has good efficacy in the treatment of psoriasis, while the side effects such as erythema, pigmentation, DNA damage and carcinogenesis are small. Narrow-spectrum UVB treatment is superior to broad-spectrum UVB and safer than PUVA treatment. The effectiveness of narrow-spectrum UVB is the same as the early stage of PUVA, but the remission period is not durable. Narrow-spectrum UVB can be used alone or in combination with some topical preparations and internal drugs. It is one of the more widely used phototherapy for all types of common psoriasis. Use with caution in patients with erythrodermic and pustular psoriasis.