Objective The characteristics of nosocomial infection outbreak were analyzed and the causes were discussed. Methods Pharyngeal swabs, serum samples and air conditioning circulating water outside the ward, bath water in the room, circulating water in the doctor's office and roof air conditioning system were collected in hospital infection cases. IgM of legionella pneumophila and influenza virus nucleic acid were detected in pharyngeal swabs and serum samples, and the water samples were collected for the culture of legionella pneumophila.Serum indirect immunofluorescence assay was used to determine IgM and bacterial culture of legionella pneumophila.Reverse transcription polymerase chain reaction (PCR) was used to detect nucleic acid and genotyping of influenza virus. Results All the cases of this epidemic occurred in the endocrinology department of the hospital, and 10 patients were reported in total, mainly respiratory symptoms. The epidemic lasted for 9 days, and the patients were 71 to 87 years old, mainly hospitalized patients, a total of 6 cases.There were 4 cases of illness among medical staff, aged 24~ 37 years.Serum IgM antibody (+) of legionella pneumophila in 7 patients; The culture of legionella pneumophila in condensed water, circulating water and pharynx samples was negative. Influenza virus nucleic acid positive in 5 cases (H₃N₂). Conclusion This may be an outbreak of nosocomial infection caused by legionella pneumophila combined with common seasonal influenza virus infection.