A pigmented nevus, also known as a dark mole, colored nevus or nevus, occurs mostly in childhood, but also from birth. Most of them are yellow, brown or black in color, but there are also blue, purple or colorless ones, which are benign tumors containing nevus cells. Pathologically, pigmented nevi can be divided into junctional nevi, mixed nevi, and intradermal nevi. Although most people have nevi, and the probability of malignant transformation (also known as carcinoma or malignant black, malignant melanoma) is very small, but the key to the problem is that the majority of patients should have an understanding of this type of disease, and really do to prevent the problem before it occurs. In recent years, the incidence rate of malignant melanoma in Chinese people has been increasing year by year. Due to the rapid growth of malignant melanoma, high malignant degree, easy to early metastasis and lack of effective treatment, it has become one of the first fatal diseases of skin tumor. At present, the most effective treatment is still early diagnosis and active and effective surgical resection of primary foci, which plays a decisive role in prognosis and reducing mortality. What kind of pigmented nevus is more prone to malignant transformation? Pigmented nevus suddenly becomes darker in color, larger in size, with blurred boundary, even with pseudopods, forming elevated nodules, with rough surface and reddish surrounding; the nevus suddenly turns black, decoloration and hair loss; the nevus repeatedly breaks, bleeds, erodes, oozes, scabs and gets infected; lymph nodes around the nevus are enlarged; new small black dots (satellite foci), black halos or pigmented nodules appear within 2 cm around the nevus; at the same time. patients with localized itching, burning and painful discomfort; and the appearance of new colored nevi in the elderly. In contrast, nevi growing on friction-prone areas such as palmoplantar, soles of feet, fingers (toes), under nails (pigmented stripes), waist, shoulders, genitals, mucous membranes and so on are at risk of malignant transformation; and some researchers report that junctional nevi are more likely to develop malignant transformation. In conclusion, if a colored nevus shows the above danger signals, it should be examined by dermatoscopy as soon as possible to avoid delaying its condition. In China, we were the first to develop “Polarized light dermoscopy” (equivalent to ultrasound of the skin), which is a non-invasive examination of skin lesions, and has achieved satisfactory results in diagnosis and differential diagnosis of nevus, pigmented nevus malignant transformation, seborrheic keratosis, subnail lesions, basal cell carcinoma, carcinoma in situ, malignant melanoma, etc. This program can greatly reduce the number of patients who have to go to the doctor blindly to see a doctor. This project can greatly reduce the medical trauma such as blind biopsy and physical therapy, and provide an important basis for early diagnosis, differential diagnosis and effective treatment of clinical pigmented lesions.