We summarized the epidemiological investigation results of the first case of human infection with avian influenza A(H9N2) virus in Chengdu,China,in order to provide references for dealing with similar diseases scientifically in the future.The methods of field epidemiology and laboratory testing were used to collect the H9N2 case's clinical and epidemiological data,as well as collect and test the samples of the H9N2 case and the relevant environment,so that the possible sources of infection,the epidemiological characteristics and clinical features could be analyzed.Results showed that the H9N2 case contacted with poultry within 10 days before the onset of illness and the H9N2 virus nucleic acid was detected in the patient's specimen by PCR.This case suffered from several chronic diseases for a long time,although active treatments were taken this time,she died soon after onset.Her living environment,the chicken leftovers from cooking,and surrounding poultry markets were polluted by H9 avian influenza virus.Through the investigation,we could deduce that the infection source of this case was the chicken infecting H9N2 viruses from surrounding poultry markets.This would be the first fatality associated with influenza A (H9N2) virus infections in humans.And though avian influenza A(H9N2) virus was low pathogenic,infection could cause severe symptoms or death in people with severe underlying diseases.