Lymphedema of the upper extremities after radiotherapy for breast cancer occurs mostly in patients treated with postoperative adjuvant radiotherapy. Because of the abnormal appearance and upper extremity dysfunction, patients have to endure long-term pain in life, so it is important to pay attention to prevention and treatment. Upper limb edema is often associated with the following factors: ① The mode and operation of surgery. The incidence of upper limb edema is 16.7-70% in patients after radical surgery; it can be reduced by 1/2-2/3 in those with modified radical surgery, and some data reported that the edema is related to the extent of axillary lymph node dissection, and the incidence of edema is 36% in those with complete dissection and only 6% in those without complete dissection. Upper limb edema is also related to surgical operation and wound healing, such as postoperative incisional blood and fluid accumulation, excessive flap suture tension and flap necrosis, as well as those with a history of recurrent cellulitis, are prone to edema. ②The site and dose of radiotherapy. The phenomenon of radiation therapy-induced edema in the upper limbs is very obvious, and the incidence of edema is high in those with irradiation in the axillary area; the incidence of edema is low in those without irradiation. In patients with complete axillary lymph node dissection, edema can occur in 72% of patients with axillary dose over 46Gy, while edema can occur in only 19% of patients with dose less than 46Gy. (③) Obesity. The high incidence of upper limb edema in obese patients may be due to the fact that obese patients are more prone to paracutaneous fat necrosis and prone to poor wound healing and infection. (iv) Advanced age. Edema is associated with obstructed lymphatic drainage, and the compensatory capacity of lymphatic return decreases with age as the lymphatic vascular-venous short circuit is gradually reduced. The mechanism by which upper limb edema occurs is that a portion of the lymphatic vessels are cut off during axillary lymph node dissection, and lymphatic fluid is returned mainly by compensatory mechanisms such as new lymphatic vessels and new traffic branches. Under normal circumstances, these compensatory mechanisms can basically satisfy the lymphatic fluid return in the physiological state, but if factors that impair the compensatory mechanisms or increase the load on the lymphatic vessels occur, upper limb edema is more likely to occur. After radiotherapy, the narrowing or occlusion of microscopic lymphatic vessels and fibrosis of subcutaneous tissues obviously restrict the lymphatic fluid return, and this causes thickening and sclerosis of the lymphatic vessel walls and fibrinogen emboli in the lumen for a long time, and the lymphatic fluid return is further obstructed, in which case, streptococcal infection is likely to occur, leading to lymphangitis and cellulitis, and the infection will further aggravate the sclerosis and obstruction of lymphatic vessels, so a vicious circle is formed, and edema becomes more and more aggravated. The prevention and treatment of lymphedema of the upper extremity should pay attention to the following aspects: ① The mode and operation of surgery should be in accordance with the standard. Since the extent of axillary lymph node dissection has a great influence on the occurrence of upper limb edema, the extent of dissection should be reduced in early cases, such as those with little possibility of axillary lymph node metastasis. If there is axillary lymph node metastasis that needs to be cleared, modified radical surgery should be used instead of radical surgery in order to better protect the compensatory function of lymphatic reflux. At the same time, surgical complications should be prevented and dealt with early. ②Accurate grasp of radiotherapy indications. For patients with thorough debulking surgery and less serious lymphatic metastasis, especially those limited to the level below the pectoralis minor muscle, the axilla can be left unilluminated. For those whose cancer is located medially, the focus of radiotherapy is the medial breast area rather than the axilla. For patients with large primary foci and no or very few lymph node metastases, the main purpose of radiotherapy is to prevent chest wall recurrence, and the amount of axillary irradiation need not be too large. ③ Timely and reasonable functional exercise of upper limbs. Avoiding prolonged drooping, pressure, trauma and infection of the affected upper limb can reduce the factors of increased lymphatic exudation or obstructed lymphatic return in the upper limb. ④Early preventive measures for edema. Elevating the affected limb and performing centripetal massage; or wearing mechanical methods such as tight-fitting clothes have some effect. ⑤ Diuretics have short-term efficacy, but long-term use is not effective. Because they cannot change the pathophysiological process of the disease, they should not be commonly used. ⑥For those who have serious edema and the function of the affected limb is seriously affected by the ineffective non-surgical treatment, surgical reconstruction of lymphatic vessels can be considered.