Nail black line is also called nail black line, the reason for its formation is not only related to nevus of mother nail, but also may be related to nail melanoma, and the treatment is mainly based on observation and surgical treatment. 1. Nail nevus: It is a kind of benign pigmented nevus that occurs in the nail area, and nail black line is its typical manifestation, and the method of removing it mainly lies in surgical treatment. Since it does not affect the body, it is usually observed. 2. Nail melanoma: it is a kind of malignant tumor, which is usually transformed from nevus of nail, due to the high degree of malignancy, it needs timely surgical treatment, supplemented with chemotherapy and radiotherapy if necessary. Due to different causes and different treatment methods, the specific situation needs to be referred to the doctor for an interview.