Abstract: Objective To understand the epidemiological and clinical characteristics of the severe acute respiratory infection (SARI) cases in hospital and their infection status of influenza virus. Methods The epidemiological survey was conducted among the SARI patients hospitalized in the first hospital of Changsha (the sentinel hospital), and throat swabs were collected from them for influenza virus nucleic acid detection by using real-time RT-PCR. Results From November 2009 to December 2010, 179 patients were surveyed, who were mainly from pediatric wards, respiratory disease wards and neurological wards. Totally 122 cases occurred from the 48th week of 2009 to the 3rd week of 2010. The median age of the cases was 38 years (0-90 years). The differences on the proportions of confirmed influenza cases among SARI cases in different age groups had statistically significance (2=20.321, P=0.002), and the proportion in age group of 5-14 years was highest (62.50%); 53 cases were influenza virus nucleic acid positive, the positive rate was 29.61%. Among the influenza cases, 41 (77.36%) were the cases of A (H1N1) pdm 09 with the highest incidence of complication due to pulmonary infection (56.42%). The difference on the incidence of complications between positive group and negative group in the viral nucleic acid detection had no statistically significance. Conclusion The severe acute respiratory infection surveillance can expand the surveillance of influenza and provide scientific evidence for the control and prevention of influenza.