The mammary gland is the lactating organ of women and normally secretes milk only during lactation. Many patients are deeply alarmed by the discovery of unexplained nipple overflow. In fact, there are many causes of nipple overflow, which can be physiological or pathological. Certain systemic diseases can cause nipple overflow, such as pituitary tumors, hyperthyroidism or oral hormonal drugs; non-neoplastic breast diseases such as ductal dilation, milk retention, various types of ductal inflammation; and neoplastic lesions of the breast such as intraductal papilloma and breast cancer can cause nipple overflow. In the past, clinical diagnosis was made through pathological diagnosis of overflow smear, mammography and other techniques, and if the diagnosis could not be confirmed, surgery would be performed for further diagnosis. A variety of benign and malignant diseases of the breast can manifest as nipple discharge, such as lobular hyperplasia, ductal dilatation, milk retention, intraductal papilloma or intraductal papillomatosis, and breast cancer (including intraductal carcinoma and lobular carcinoma in situ), among which intraductal papillomatosis is a pre-cancerous lesion of the breast. The clinical diagnosis of nipple overflow is a prerequisite for further treatment. Ductal endoscopy not only greatly improves the diagnostic accuracy of the cause of nipple overflow and enables patients to avoid unnecessary surgery, but also overcomes the shortcomings of mammography and other conventional examinations that are difficult to confirm the diagnosis. Ductoscopy is a new diagnostic method that is both fast and accurate in the diagnosis and treatment of nipple discharge. Ductoscopy is a miniature endoscope with a diameter of less than 1 mm, which can be inserted into the milk duct through the small hole where the patient’s nipple overflows. With the help of ductoscopy, the doctor can observe the lesion in the milk duct at a glance, and if it is a patient with duct dilatation or inflammation of the milk duct, the nipple overflow can be terminated after local irrigation by fiber ductoscopy; and cell smear or biopsy can be performed immediately on the suspected lesion site under the mirror. This technique is simple, safe, and less painful for the patient, and is an economical and effective clinical diagnosis and treatment technique.