Child hyperthyroidism is one of the most common pediatric endocrine diseases, and often be misdiagnosed or missed diagnosed due to its atypical symptoms in the initial stage. Child patients with undiagnosed hyperthyroidism are more likely to present thyroid crisis, with a mortality of 8%-25%. This study reports a case of thyroid crisis in a child patient with undiagnosed hyperthyroidism after cardiac surgery, and discusses the experience of perioperative management, which provide evidence for anesthetic management of such child patients.