The etiology of dark watery vaginal discharge is due to the presence of melanoma in the vagina. Vaginal melanoma should be distinguished from other rare melanin-containing tumors such as pigmented neurofibromas and malignant nerve sheath meningiomas. Vaginal melanoma is characterized by a variety of cell types, especially unpigmented vaginal melanoma, which is easily misdiagnosed with squamous vaginal carcinoma, vaginal adenocarcinoma, and sarcoma, with a misdiagnosis rate of 20%. Vaginal melanoma has typical clinical manifestations. Gynecological physical examination reveals vaginal lesions, it is relatively easy to obtain a clinical diagnosis, and the suspects can be pathologically examined by punch biopsy or excision of the whole lesion. The cutting edge includes 1 to 2 cm of normal vaginal mucosa to prevent the spread of the tumor during biopsy, and the resected tissue is confirmed by rapid freezing examination to expand the scope of the operation according to the situation, and the cytological smear of the vagina can help in the rapid diagnosis of the disease. The smear can see non-epithelial malignant tumor cells. So, how to prevent vaginal discharge with black watery color? The following are the preventive methods of vaginal discharge with black watery color: 1, active treatment of diseases, such as vaginal leukoplakia, chronic inflammation and ulcers. 2, where there is irregular vaginal bleeding, abnormal leukorrhea, early clear diagnosis, active treatment.