The appearance of black spots on the arm should be considered pigmented nevus, seborrheic keratosis, flat warts, hyperpigmentation and other diseases, according to different causes of treatment. 1. Pigmented nevus: it is a kind of benign tumor containing nevus cells, preferably occurring in mucous membrane and skin, and can be manifested as black spots on the arm. Generally, it does not need surgical treatment because it has little possibility of malignant transformation. 2. Seborrheic keratosis: it is a kind of degenerative skin changes in the elderly, also known as age spots. It can be found on the arms, face, trunk and other parts of the body. And it will increase with age. The main manifestation is the appearance of black spots on the arms. 3. flat warts: black flat papules appear on the skin surface due to human papilloma virus infection. It can be treated with carbon dioxide laser or liquid nitrogen freezing. 4. Hyperpigmentation: such as ultraviolet radiation, endocrine, digestive system diseases, can lead to black spots on the arm. It can be treated with topical application of vitamin E cream or laser treatment. If the above factors exist, it is recommended to go to the hospital to identify the cause of the disease, standardized treatment under the guidance of the doctor, the use of drugs need to follow the doctor’s instructions, so as not to delay the condition.