On November 29，2018，an outbreak of suspected African swine fever（ASF）took place in a swine farm in Tianjin City，and the infected pigs suffered from anorexia，increasing body temperature，acute death and other symptoms，which was finally confirmed as ASF by National Laboratory of Exotic Animal Diseases Research Center. Immediately，an emergency epidemiological investigation was carried out by means of field questionnaire survey，informal discussion，sampling for laboratory test and data analysis by the experts from an epidemiological investigation team，subsequently，the distribution of time，regional and population of the epidemic was described to identify all risk factors，infer all causes of the outbreak and to put forward corresponding suggestions. Based on the spreading characteristics of ASFV and the results of field investigation，laboratory test and data analysis，it was concluded that the outbreak was caused by the major risk factor that kitchen wastes containing pork sausage products were fed to the pigs，however，the possibility of spreading via persons and vehicles carrying the virus should not be ruled out. The outbreak was effectively controlled by appropriate measures，and no any spread of pathogens was observed. In addition，the importance for prevention and control of ASF through implementing the ban on feeding with kitchen wastes and strengthening management and disinfection for vehicles transporting pigs was verified by this investigation.