Background: On February 18, 2009, 70 people were poisoned by clenbuterol in Guangzhou city, and many people were shocked by "clenbuterol". According to the introduction of Guangzhou Food Safety Office, the hogs that caused this "clenbuterol" poisoning case were respectively purchased from several areas of Lengshuijiang city, Liuyuan city, Xinhu county and Hengyang county by hog individual operators, then they entered Guangzhou through Tianhe livestock wholesale market.