Objective To investigate the relationship of pneumonia severity index(PSI) and etiology of patients with community-acquired pneumonia(CAP),  in order to provide a basis for empirical antibiotic therapy in emergency. Methods The clinical data of patients with CAP admitted to the Emergency Department of Beijing First Hospital of Integrated Chinese and Western Medicine were retrospectively analyzed. The patients were divided into low risk group and high risk group according to PSI. The data including gender, age, history of disease, etiology and prognosis were compared among groups. The correlations between PSI score and etiology were analyzed. Results A total of 367 patients with CAP were enrolled with 197 low risk group and 170 high risk group, and the 30-day mortality was 21.8%(80/367).  The age and proportion of men in high-risk groups were significantly higher than those in low-risk groups.  The history of diabetes，cerebrovascular history, cardiovascular disease, and the prevalence of tumors in high-risk groups were significantly higher than those in the low-risk group.  The most common strain of the low-risk group was mycoplasma（P＜0.001），The high-risk groups were more likely to see KNP (P=0.039) and P. Aeruginosa, There was no significant difference between the two groups of streptococcus pneumoniae and other pathogens. Mortality of High-risk group was significantly higher than those in the low-risk group（44.7% vs. 2%，P＜0.001). The most deaths occurred in patients with pneumococcus pneumoniae, pseudomonas aeruginosa, pneumoniae pneumoniae, and patients who had no positive findings. Conclusions The different risk stratification of patients with community-acquired pneumonia has different pathogen profiles.