Objective To investigate the accuracy of continuous glucose monitoring (CGM) system in emergency critically ill patients. Methods Critically ill patients admitted to the Intensive Care Unit of Department of Emergency Medicine, West China Hospital of Sichuan University between August 2022 and February 2023 were continuously enrolled. Blood glucose monitoring was performed using CGM system, while blood glucose in the patient’s fingertips was monitored every 4 hours. The correlation and consistency of blood glucose values between CGM system and fingertip glucose detection were compared. Results A total of 52 patients were included, and 1 504 matching blood glucose pairs were formed with fingertip blood glucose values. The overall correlation coefficient was 0.874 (P<0.001), the mean absolute relative difference was 14.50%, and the highest mean absolute relative difference (31.76%) was observed in the hypoglycemic range (<3.9 mmol/L). The percentage of CGM system blood glucose within ±15%, ±20% and ±30% of fingertip blood glucose was 56.65%, 75.56% and 94.75%, respectively. The intra-group correlation coefficient between CGM system blood glucose and fingertip blood glucose was 0.85 on the consistency test, and the Bland-Altman plot showed acceptable clinical accuracy. Conclusions The overall accuracy of the application of CGM system in critically ill patients is reasonable, but the accuracy in the range of low blood glucose values is poor. Whether the auxiliary use of CGM system can improve the blood glucose management of critically ill patients and reduce medical costs needs to be further studied.