Abstract: Objective: To explore the feasibility and applicability of Modified Early Warning Score (MEWS) in predicting prognosis of emergency potential critical patients. Methods: The data of 670 outpatient patients were recorded and scored with MEWS between February and March, 2014, and all patients' prognosis (survival, death) were followed up. The correlation of MEWS score and patients prognosis were statistically analyzed. The MEWS scores of survival and death patients were compared as well as area under of ROC curve of MEWS in these indexes. Results: MEWS had a positive correlation with the patient prognosis, the correlation coefficient was 0.47, and P<0.05. When the death as the predictive index, the best cut-off of MEWS grade was 7, sensitivity 94%, specificity 94%, positive predictive value 58%, negative predictive value 99%, the area under the ROC curve: Az = 0.947 (95% CI: 0.911, 0.983).Conclusion: MEWS have high predictive value of patients' prognosis, and have ability to estimate the severity of the emergency patients. MEWS is suitable for the emergency patients because its grading operation is simple and quick, low cost, and fast dynamic assessment of patient's condition.