The severity of a cystic nodule in the left lobe of the thyroid gland can generally be objectively evaluated based on factors such as the size and nature of the nodule. If a cystic nodule in the left lobe of the thyroid gland is more than 5 cm in size, a large nodule may compress the trachea and esophagus, causing breathing difficulties at night and even serious complications such as asphyxia. If the nodule is serious, it is recommended that the patient undergoes surgery to remove it as soon as possible. If a cystic nodule of the left thyroid gland is accompanied by a large amount of blood flow signal, longitudinal to transverse ratio greater than one, unclear boundary, uneven echogenicity and other signs of malignant tumor, the nodule is likely to become cancerous. Cancer cells may invade the surrounding organs and tissues along the surrounding blood vessels and lymphatic vessels, which may also cause serious complications. In this case, patients are also recommended to undergo surgical excision plus lymph node clearing as soon as possible, and post-operative combination with iodine-131 radiotherapy can achieve almost radical effect after surgery for patients with early disease.