Abstract: Photodynamic therapy(PDT) is a new therapy on port wine stains. The mechanism include the interaction of lights, photosensitizer and the production of oxygen. The vascular endothelial cells in the lesion are damaged by PDT, while the epidermis and the blood vessels in the deep dermis are ignored. PDT selectively closes the target vessels and show a good clinical effect. The main side effect of PDT is the photosensitizing due to the using of photosensitizer.