The incidence of malignant melanoma is not very high in clinical practice, especially when it occurs after trauma to the extremity, it is difficult to draw attention to it in the early stage, and it is easy to be misdiagnosed; some patients who have not been traumatized, but have nail bed thickening and gray color under the finger nail, are easily treated as gray nail, which results in delaying the disease. Crossborder nevus: nevus cells are located in the basal cell layer and extend to the subepidermis. The area is flat and darkly pigmented. The nevus cells are easily irritated and are susceptible to malignant transformation by local trauma or infection. Mostly located in the hands and feet, vulnerable to trauma. Pre-malignant manifestations of nevus: the boundary of nevus is blurred within a short period of time and increases rapidly; the base of nevus appears radiolucent or burr-like, with jagged edges and deepened or changed color; the nevus is locally prickly, burning or painful, with an orange peel-like appearance, a small amount of exudate at the edge, the outline of the original spot surface rises, fades, bleeds, crusts or forms small ulcers; scattered satellite nodules appear around the original nevus. There are four types of nevi as follows: 1. Freckle type: the least malignant. Prevalent on the head, neck and back of hands. They appear as large, flat or brown lesions slightly above the skin surface. 2. Superficial spreading type: It occurs around 50 years old, mostly on the limbs in women and on the trunk in men. They appear tan, brown, blue or black, most of them can be rosy or peachy red, with jagged edges and loss of skin texture. 3, nodular type: the highest degree of malignancy, preferably in the back. The nodules are gray with a peach color, and when the lesions continue to grow, their color becomes blue-black, and ulcers and metastases occur earlier. 4.Pigmented melanoma: It mainly occurs on the palms of hands, soles of feet and under the nails, and becomes brownish-yellow or brownish-brown, and if left untreated, the lesion will be nodular and elevated. A nevus may become malignant and turn into malignant melanoma if it is stimulated by repeated friction, trauma, improper surgery, etc. Malignant melanoma is a tumor with a fairly high degree of malignancy, and metastasis can occur at an early stage of the tumor. Most of them have clear trauma, and the symptoms after trauma cover up the signs of malignancy, so they often continue to be treated as trauma; general surgeons, especially orthopedic surgeons, often lack due vigilance, and non-oncologists, especially young and inexperienced doctors, know little about the disease, so it is difficult to think of malignant melanoma in patients with limb injuries. When symptoms appear and attention is drawn, the best time for treatment is often delayed and distant organs are already invaded and the significance of surgery is lost. Therefore, when we encounter a nevus with deepening pigment, enlargement, discomfort or pain that may be malignant, we should do complete excision in time; for limb end injury with abnormal healing and other local changes, we should think about the possibility of malignant change and make diagnosis as early as possible and perform extensive excision treatment. Malignant melanoma is not sensitive to radiotherapy and chemotherapy, so early surgery is the most important, and after surgery, it can be treated with immunotherapy, such as BCG or interleukin and interferon, but the clinical effect is not exact. So remind everyone that for this disease doctors and patients are equally important, as long as one side pays attention, it will reduce misdiagnosis and mistreatment!