Erythema nevosum, also known as wine spot, microvascular vascular malformation, capillary malformation, etc., commonly known as “red birthmark”, is a common congenital, benign, superficial dermal capillary dilation malformation that does not fade on its own. The incidence is as high as 3‰-5‰, which can occur in any part of the body, but is more common in the face and neck, manifesting as flat, well-defined pink patches at birth, increasing in size with age and body growth, gradually deepening in color to red and purple, thickening of the tumor body, partly nodule-like changes, a few cases of hyperplastic nodules can be grape-like or verruciform, or even extremely dilated and sagging. Without treatment, the nodules will generally remain with the patient for the rest of his or her life, which has a serious impact on the patient’s psychology and quality of life. Photodynamic therapy (PDT), formerly known as photoradiation therapy and photochemotherapy, is commonly known as injecting a drug (photosensitizer) into the body and then using laser irradiation to stimulate the photochemical effect of the drug, thereby destroying the lesioned tissue to achieve the purpose of removing the lesion. Photodynamic treatment of erythema nodosum realizes selective closure of lesion blood vessels, which can eliminate lesions while protecting normal skin tissues to the maximum extent, and its efficacy greatly surpasses foreign pure pulse dye laser treatment, solving the problem of scarless treatment of the disease, which is a new treatment of erythema nodosum with high selectivity, good efficacy, safe and reliable, and has achieved good clinical effect, thus becoming It is a new treatment for the scarless treatment of the disease, which is selective, effective, safe and reliable.