On October 25，2021，some beef cattle suddenly died in a farm in Xuanhan County，Sichuan Province. In order to investigate the event and find out all the causes leading to the death，and to take measures to reduce economic loss of the farm as far as possible，an epidemiological investigation was carried out on the farm. It was investigated that a total of 22 cattle died within three days，with a cumulative mortality rate of 46.8%（22/47）. It was preliminarily speculated that，based on the information of movement，clinical symptoms and changes under autopsy，the cattle died of aflatoxin poisoning due to feeding with moldy feed. The disease was effectively controlled after stopping feeding the previous feed，increasing the amount of drinking water，changing forage and adding montmorillonite. It was suggested that the farm staff should learn the knowledge about breeding management and disease prevention and control，strengthen their sense of responsibility and improve their ability for feeding and management.