Breast cancer is one of the most common malignant tumors in women, and its high incidence is between the ages of 40 and 55. The following categories belong to the vulnerable groups of breast cancer: those who have a family history of cancer, especially those whose mothers or sisters have had breast cancer; those who have early menarche (under 12 years old) and late menopause (above 55 years old); those who have certain benign breast diseases; those who have never breast-fed, never given birth or given birth too late or had many abortions. In order to detect breast cancer at an early stage, especially middle-aged women should frequently check themselves for the presence of lumps in their breasts and go to the hospital for further examination and diagnosis in time if they find any abnormality, so that they will not miss the best time to treat breast cancer. The best time for breast cancer self-examination is one week after the end of menstruation, and if the menstrual cycle is irregular, it is better to perform self-examination at the same time of the month. The American Cancer Society (ACS) recommends three methods of breast self-examination: a. Visual inspection in bright light, stand upright in front of the mirror and take off your shirt, cross your arms and elbows backwards, so that your chest muscles are tense, and compare both breasts in front of the mirror to observe whether the bilateral breasts are symmetrical and whether there are any abnormal changes in shape, size and outline; whether there is redness, rash, skin folds and orange peel-like changes in the breast skin; whether the bilateral nipples are at the same level and whether there are any abnormal changes in the breast skin. Whether the nipples are at the same level, whether there is elevation, retraction, depression, and whether there is abnormal discharge from the nipples; whether the areola color has changed. The left and right breasts should be examined in steps. Check the left breast: raise the left arm and touch the breast slowly, steadily and carefully with the three fingers of the right hand (index finger, middle finger and ring finger), taking care not to grasp and pinch with the fingers. Move the left breast clockwise from the outside to the inside in a gradual manner, at least three circles from the periphery of the breast to the nipple. Then gently squeeze the nipple with the thumb and index finger to observe for nipple drainage. If a cloudy, yellowish or bloody discharge is found, seek immediate medical attention. The right breast is examined in the same way as above. Third, lying down check lying down check, take the supine position, right arm raised above the head, right shoulder under a small pillow, this position makes the breast flat, easy to check. The examination method is the same as that of palpation, and then the same method is used to examine the left breast. The earlier breast cancer is detected, the greater the chance of cure. If you find any abnormality, you should go to the hospital for further examination so that early detection, early diagnosis and early treatment can be achieved.