Abstract: Objective To investigate the difference of pituitary and thyroid hormone levels in ICU critical patients and further analyze the relationship between hormone levels and gender, brain lesions, acute physiology and chronic health status(APACHE Ⅱ) scores. Methods A total of 120 critically ill patients admitted to the ICU ward of our hospital from January 2013 to June 2018 were enrolled. The APACHE Ⅱscore was used to assess the severity of the disease. The thyrotropin(TSH), free triiodothyronine(FT3), free tetraiodothyronine(FT4), and growth hormone(GH) in the serum were tested. The hormone levels of the male group and the female group, brain lesion group and non brain lesion group, Apache Ⅱ scores ≤ 15 group and Apache Ⅱ scores>15 group were compared according to gender, presence or absence of brain injury and cerebrovascular disease, Apache Ⅱ score. The correlation between hormone level and gender, brain lesions, Apache Ⅱ score in critical patients were analyzed by Pearson correlation coefficient analysis. Results The FT3 of the male group were higher than that of the female group(P<0.05). The FT3 and FT4 of the craniocerebral injury group were higher than those in the non craniocerebral injury group(P<0.05). The FT3 and FT4 levels in the APACHE Ⅱ scores>15 group were lower than those of APACHE Ⅱ scores ≤ 15 group(P<0.05). The results of correlation analysis showed that FT3 was correlated with the gender and craniocerebral injury of ICU critical patients, and negatively correlated with their APACHE Ⅱ scores. Conclusion In addition to gender differences, FT3 is related to the brain lesions and APACHE Ⅱ scores of ICU critical patients. The FT3 can indirectly reflect the severity of the disease and predict the high-risk risk. Thyroid hormone can be used as the evaluation indexes of the severity of craniocerebral injury.