Objectives The possible source of a family member of a sheep farmer in Shangluo City, Shaanxi Province diagnosed with brucellosis was determined and the risk of spread was assessed to provide a basis for the prevention and control of brucellosis among livestock. Methods A working team was set up in Shangluo Animal Disease Prevention and Control Center together with relevant departments on July 3, 2023 to carry out an emergently epidemiological investigation of brucellosis among livestock in a village in Luannan County, Shangluo City with on-site investigation, discussion, laboratory testing and other methods. Results The results of Rose Bengal plate agglutination test and tube agglutination test used to detect all the adult sheep in the village were negative, indicating that the introduction of brucellosis-infected sheep by the sheep farmer and the direct mixed rearing after introduction are the main causes of the disease in other sheep in the farm. Conclusions It is recommended to strictly implement the isolation and quarantine system for sheep, increase efforts of surveillance and monitoring, do a good job in monitoring of animal diseases, and strengthen publicity and education, actively carry train the knowledge about the prevention and control of brucellosis.