Objective To evaluate the value of National Early Warning Score 2 (NEWS2) combined with arterial blood lactic acid (Lac) level in predicting short-term prognosis of patients with severe community-acquired pneumonia (SCAP). Methods Data about neutrophil-to-lymphocyte ratio (NLR), oxygenation index, NEWS2 as well as acute physiology and chronic health score (APACHE Ⅱ) of adult patients with SCAP admitted to a tertiary first-class hospital from May 2017 to May 2022 were collected retrospectively. According to the 28-day prognosis, patients were divided into survival group and death group. Differences between two groups were compared, and correlation of main indicators were analyzed. Multivariate logistic regression analysis and receiver operating characteristic (ROC) curve were adopted to analyze the predictive value of NEWS2, Lac and their combination on the risk of death in SCAP patients. Results A total of 97 SCAP patients were enrolled, 65 survived and 32 died, with a 28-day mortality of 32.99%. Compared with survival group, NEWS2 score, APACHE Ⅱ score, procalcitonin (PCT), NLR and blood Lac increased significantly in death group, while CD3⁺CD4⁺ T lymphocyte and oxygenation index decreased significantly, with significant differences. Blood Lac had a good correlation with NEWS2 and APACHE Ⅱ (r=0.411, 0.709, both P < 0.01). Multivariate logistic regression analysis showed that NEWS2 and blood Lac were independent risk factors for 28-day mortality in SCAP patients (OR=1.422, 95%CI 1.043-1.938; OR=1.635, 95%CI 1.072-2.492, both P < 0.05). ROC curve analysis showed that compared with the traditional APACHE Ⅱ score, NEWS2 and blood Lac had good predictive value for 28-day mortality of SCAP patients (area under the curve [AUC]: 0.740, 0.721 vs 0.772, Z=0.506, 1.141, both P>0.05). When the best cut-off values of NEWS2 and blood Lac were 7 points and 1.96 mmol/L respectively, the sensitivity were 81.3% and 68.7%, the specificity were 63.1% and 75.4% respectively. The combination of NEWS2 and Lac showed higher predictive va-lue (AUC: 0.776 vs 0.772), with higher sensitivity (84.4%) and specificity (70.8%). Conclusion NEWS2 and blood Lac at admission are independent risk factors for the 28-day mortality of SCAP patients, both had high predictive value. NEWS2 combined with blood Lac has higher predictive value in short-term prognosis of SCAP patients than single score.