Objective: To investigate the relationship between thyroid function and ventilator weaning in patients with invasive mechanical ventilation, and to evaluate the correlation and significance of thyroid function and ventilator weaning outcome. Methods: A total of 126 critically ill patients admitted to ICU of Gaoming Hospital Affiliated to Guangdong Medical University from January 2018 to December 2020 with invasive mechanical ventilation time>48 h and thyroid function test were selected.According to whether invasive mechanical ventilation was needed within 24 h after extubation, they were divided into successful weaning group and failure weaning group.The age, mechanical ventilation time, Acute Physiology And Chronic Physiology (APACHEⅡ) Score and thyroid function test results of the two groups were recorded and compared. Results: Among 126 patients with invasive mechanical ventilation, 86 cases were successfully withdrawn and 40 cases were failed.The levels of free triiodothyronine (FT3) and free thyroxine (FT4) in the successful weaning group were significantly higher than those in the failure weaning group (P＜0.05); there was no significant difference in the levels of total triiodothyronine (TT3), total thyroid hormone (TT4) and thyroid stimulating hormone (TSH) between the successful weaning group and the failure weaning group (P＞0.05).Logistic multiple regression analysis showed that FT3 and FT4 levels were the protective factors for weaning failure in patients with invasive mechanical ventilation. Conclusion: The level of thyroid function in patients with invasive mechanical ventilation is related to the severity of the disease.The low level of FT3 and FT4 is one of the important reasons for weaning failure.