A small proportion of lung cancer patients may develop hyponatremia in early stage, with clinical manifestations such as nausea, vomiting and weakness, which is mostly seen in small cell lung cancer, and is a manifestation of paraneoplastic syndrome, caused by the abnormal increase of antidiuretic hormone secretion. In 1938, Wilker et al. first found that hyponatremia was associated with lung cancer, and in 1957, Schwartz et al. again found that patients with bronchial lung cancer had hyponatremia with massive renal sodium excretion, which was thought to be caused by abnormal increase in secretion of antidiuretic hormone and named SIADH. more than 60 diseases with SIADH have been found so far, but most of them are Most of them are malignant tumors, with lung cancer being the most common, of which small cell lung cancer accounts for 90%. The best treatment for SIADH is to actively diagnose the cause and treat the original disease. The combination of SIADH with tumor can be normalized with the resection of the tumor and the efficacy of radiotherapy. It has been reported that patients with small cell lung cancer combined with SIADH are in remission after chemotherapy without restricting water intake and without SIADH symptoms. The main goal of SIADH treatment is to correct hyponatremia, and the treatment is divided into two stages: “emergency correction of hyponatremia” and “correction of chronic hyponatremia”. Blood sodium