Objective To analyze the epidemiological characteristics and risk factors of an outbreak of influenza A H1N1 in a specialized psychiatric hospital in Shantou City, Guangdong Province, provide scientific basis for the prevention and control of respiratory infectious diseases in psychiatric health institutions. Methods Data of infection cases in this hospital in May 1-27, 2024 were collected with on-site epidemiological investigation method, and were analyzed with descriptive epidemiological methods. The specimens of the cases were performed nucleic acid testing by reverse transcription polymerase chain reaction (RT-PCR) method. Results A total of 43 influenza-like cases in this outbreak have been reported, with an incidence of 16.67%, including 42 hospitalized patients and 1 healthcare worker. Among the 42 hospitalized patients, there were 41 males, with an incidence of 35.04% and 1 female with an incidence of 2.22%, there was a statistically significant difference in incidence between hospitalized patients of different genders (χ²＝18.23, P＜0.001). The epidemic curve shows that after the first case appeared on May 8, 2024, the number of cases increased significantly from May 13, and reached its peak on May 17 (n=17). 31 patients’ throat swab specimens were collected, out of which 29 (93.55%) were positive for influenza A H1N1 virus nucleic acid and 2 (6.45%) were negative. Conclusion This epidemic is an outbreak of influenza A H1N1 in a psychiatric health institution, the epidemic curve shows a point source human-to-human transmission mode. Failure to effectively identify and isolate cases in the early stage can lead to the spread of the epidemic across floors and wards. It is necessary to regularly organize hospitalized patients and healthcare workers to receive influenza vaccines, strictly implement the health monitoring system, strengthen the control of external personnel, and enhance the early detection and emergency response capabilities for infectious disease outbreaks.