Flap necrosis and subcutaneous fluid accumulation after radical or modified radical mastectomy are common complications that seriously affect the patient’s postoperative recovery process. Subcutaneous fluid makes the flap float, increases the tension of the incision, reduces the blood flow of the flap, affects the healing of the incision, and easily induces infection, which leads to or aggravates the necrosis of the flap, delays the implementation of postoperative radiotherapy, chemotherapy and other comprehensive treatment measures, and increases the risk of recurrence and metastasis after surgery. Reducing the occurrence of postoperative subcutaneous fluid is related to improving the survival quality of patients, and the causes and prevention measures of flap necrosis and subcutaneous fluid formation are now discussed with clinical data.