The cause of black watery vaginal discharge is due to the presence of melanoma in the vagina. Vaginal melanoma has a typical clinical presentation. The clinical diagnosis is easier to obtain when a vaginal lesion is found on gynecologic examination, and pathologic examination can be performed by punching a biopsy or removing the whole lesion in suspicious cases. The cut edge includes 1 to 2 cm of normal vaginal mucosa to prevent spread of the tumor during biopsy, and the excised tissue is confirmed by rapid freezing to expand the scope of the procedure according to the situation. The smear may reveal non-epithelial malignant tumor cells. So, what are the preventive measures for black watery vaginal discharge? The following are the preventive measures for black watery vaginal discharge: 1. For a woman, the easiest way to check is self-examination during bathing. For married women, regular gynecological examination should be done so that gynecological and even other gynecological diseases can be detected in time. Once you find symptoms such as enlargement, bulging, bleeding, ulceration and itching of vulvar pigmented nevus, you should go to the hospital in time for early diagnosis and treatment. 2. Pay attention to personal hygiene and keep the vulva clean. In terms of dressing, cotton underpants that are less irritating to vulvar skin and loose, soft and breathable outer pants should be used to reduce the friction on vulvar skin. 3. For patients with suspicion, a clear diagnosis should be made and attention should be paid to not to carry out local biopsy of the lesion, but to prepare for surgical excision and to remove the lesion completely, with the cutting edge more than 2-3 cm away from the lesion.