In February 2022，21 pigs successively died of unknown causes in a household in Yanchang Country of Shaanxi Province，which was confirmed to be an outbreak of anthrax as joint diagnosed by Shaanxi Center for Animal Disease Prevention and Control together with laboratories at city/county level. In order to find out the sources of the pathogen and identify all infection routes，a special working team was organized by relevant authorities at the provincial，municipal and county levels according to relevant procedures of epidemiological investigation on major animal diseases to analyze any possible sources and routes，evaluate the risk of spreading，and guide the disposal of the outbreak. It was speculated that，based on the epidemiological characteristics，clinical symptoms and laboratory microscopic examination results，the outbreak was likely to be caused by accidental exposure of anthrax bacteria in the historical infected zones then spreading via personnel，forage and vehicles. It was therefore recommended that random excavation of soil should be controlled in the historical infected zones where biosafety management should be well done in all farms，and the anthrax prevention and control of all susceptible livestock including pigs，cattle and sheep should be strengthened.