Abstract: Objective To explore the relationship between influenza A(H1N1) infection and mimune status among residents in Shaanxi province by analysis of cases distribution and serum antibody detection.Methods Time distribution of influenza A(H1N1) cases was analyzed.Two and four months a fter the epidemic peak, the hemagglutin in antibody of influenza A(H1N1) was detected in the subjects selected with random sampling.Results The epidemic pattern of influenza A(H1N1) included five periods.They were import period, epidemic period in home land, rapid amplification period, severe case occurrence period, and post period of epidemic.After the outbreak, the level of hemagglutin in antibody of influenza A(H1N1) was higher in the city than in the rural area and higher in men than in women.The persons of 617 years old had a higher level of antibody and the people of 60 years old had lower antibody level.The recessive infectious rate was 23.40%.The pure positive rate of the antibody was 25.10% after massive influenza A(H1N1) vaccination.Among the subjects with higher antibody titer than 1:20, the antibody level in vaccinated group was 1.75 to 2.52 times higher than that of in non vaccinated group.Conclusion There are 5 periods for influenza A(H1N1) epidemic.The recessive infectious rate is 23.40%.The pure positive rate of the antibody is 25.10% after influenza A(H1N1) vaccination.