Objective To explore the application of modified early warning score (MEWS) combined with temperature- adjusted shock index (ASI) in pre-hospital emergency assessment of prognosis on patients with upper gastrointestinal bleeding (UGB). Methods A total of 212 cases UGB patients who were admitted to the emergency department of Taizhou People's Hospital from January 2017 to January 2019 were collected. All patients were divided into three groups, including mild upper gastrointestinal bleeding group (blood loss < 500 ml), moderate upper gastrointestinal bleeding group (blood loss 500 to 1 000 ml) and severe upper gastrointestinal bleeding group (blood loss > 1 000 ml). The MEWS and ASI of the observation group were analyzed and the prognosis of the patients were compared. Results As the severity of UGB increasing, MEWS and ASI scores increased significantly, and there was a significant positive correlation between MEWS scores and ASI (r = 0.533, P = 0.013). With the increase of MEWS score and MEWS + ASI score, the mortality of patients increased significantly. When the cut-off value of the MEWS score was 6.3, the AUC, sensitivity, and specificity of prognostic death are 0.900 (95% CI: 0.735, 0.979), 86.67% (95% CI: 59.33, 100.00), and 80.00% (95% CI: 69.00, 100.00), respectively; MEWS + ASI are 0.980 (95% CI: 0.849, 1.000), 93.33% (95% CI: 69.00, 100.00), and 93.33% (95% CI: 69.00, 100.00), respectively. Compared with the MEWS score, the AUC, sensitivity, and specificity of MEWS + ASI score were significantly improved. Conclusion MEWS combined with ASI has diagnose value for the condition assessment and emergency treatment of pre-hospital emergency for UGB patients.