Swelling of the arm after breast surgery may be caused by obstruction of blood and lymphatic fluid return, ossification of blood vessels and nerves in the armpit. Swelling of the arm after breast surgery may be caused by obstruction of blood and lymphatic fluid return. During the operation, some of the blood vessels of the axillary vein may be cut off from their generative branches, and some of the lymphatic tissues may be cut off, resulting in obstruction of the venous return of the arm, as well as obstruction of lymphatic return, which may cause the phenomenon of swelling of the arm. Swelling of arm after breast surgery may be caused by ossification of axillary blood vessels and nerves. Postoperative ossification of axillary blood vessels and nerves leads to loss of elastic tissue support of the ductal bed, and the damage of venous intima appears as thrombosis of the upper vein, which may lead to the phenomenon of swelling of arm. In addition, tumor compression and metastasis may also appear similar clinical manifestations. Therefore, patients with arm swelling after breast surgery should go to the hospital for examination as soon as possible, and carry out standardized treatment under the doctor’s guidance after confirmation of diagnosis.