In order to find out the cause of a food poisoning case in time,the methods of epidemidogy and hygienics were adopted to investigate it and examine the suspected foods and the urine of the poisoned people. The results showed that it was caused by eating pork liver which contained clenbuterol. Through the investigation of the accident,we realize that we should strengthen the supervision of the food source and be aware of the lastest hygienic information and knowledge,which is the key to prevent and control this kind of food poisoning.