Hyponatremia caused by lung cancer is mainly considered for two reasons: First, patients with lung cancer are bedridden for a long time, eat less, are malignant and hypoproteinemic, and sodium consumption is more prone to hyponatremia, which is manifested as demented expression, slow reaction, and peripheral weakness, etc. Second, it is related to whether lung cancer is carcinoid or not. Secondly, it is related to whether lung cancer is carcinoid or not, carcinoid is the same kind of carcinoid, carcinoid is easy to cause hypokalemia and hypochloremia with carcinoid syndrome, and if lung cancer is not effectively treated, it can produce stubborn hyponatremia, which is not easy to be corrected, and it can easily lead to cerebral edema of the patient, and then death occurs. Therefore, hyponatremia of lung cancer is caused by eating less and consuming too much, in addition, it is the lung cancer itself, such as carcinoid tumors which can easily cause intractable hyponatremia, and it is necessary to resect lung lesions as early as possible to be able to correct hyponatremia.