Objective To analyze the clinical features and etiologic of community-acquired pneumonia (CAP) among the elderly aged 80 and over, and provide evidence for clinical diagnosis and treatment. Methods The clinical characteristics and etiology of the elderly CAP (≥80 years old) were analyzed by collecting and comparing the clinical characteristics and etiology between the very elderly CAP group (≥80 years old, 94 cases) and control group (65 to 79 years old, 100 cases). Results On clinical symptoms, there were statistical differences in dyspnea and gastrointestinal symptoms, systemic symptoms, and mental status (P<0.05) between the two groups. There was no statistically significant difference in upper respiratory tract symptoms, fever, cough, sputum, hemoptysis and chest pain between the two groups (P>0.05). On the complications, the very elderly CAP group was more prone to respiratory failure, sepsis, urinary tract infection and electrolyte metabolism than the control group (P<0.05). On the experimental indicators, anemia and abnormal renal function in the elderly CAP group were high (P<0.05). There was no statistical difference between the two groups of inflammation indicators (white blood count, procalcitonin, C-reactive protein, erythrocyte sedimentation rate, neutrophil alkaline phosphatase score). The pneumonia severity index score and CURB-65 score of the very elderly CAP group were significantly higher than those of the control group (P<0.001). On pathogen analysis, in the very elderly CAP group the number of bacterial infections (23/94), viral infections (21/94) and bacterial mixed virus infections (21/94) were probably equivalent, and the proportion of bacterial infections of two or more types accounted for 17.0% (16/94); The bacteria detection rate was Streptococcus pneumoniae (22.4%), Pseudomonas aeruginosa (19.4%), Stenotrophomonas maltophilia (16.4%), Staphylococcus aureus (14.9%). Viral infection mainly focused on influenza A virus (23/94) and human cytomegalovirus (21/94). Bacterial mixed virus infection was mainly caused by Streptococcus pneumoniae and influenza A virus infection. Comparing the two groups, the most common bacterial pathogen both of them was Streptococcus pneumoniae, but the overall proportion was dominated by gram-negative bacteria, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter baumannii and Klebsiella pneumoniae were more common; the gram-positive bacteria in the two groups were mainly Streptococcus pneumoniae and Staphylococcus aureus. There was no significant difference in the detection rate of above Gram-positive bacteria between the two groups (P>0.05). The two groups of virus infections were mainly influenza A virus, and the difference was not statistically significant (P>0.05). The two groups of single bacteria rate, single virus infection rate, double virus infection rate and bacterial mixed virus infection rate were similar, the difference had not been found (P>0.05). Conclusions The elderly (aged 80 and over) CAP group is prone to dyspnea, often presents with extrapulmonary atypical symptoms such as digestive tract symptoms, systemic symptoms and psychiatric symptoms, and usually accompanied with many complications. The etiological treatment mainly covers gram-negative bacteria, and we must pay attention to the possibility of combined virus infection.