Abstract: Objective To explore the characteristics and laws of an influenza pandemic and provide scientific supports for influenzas prevention. Methods The results of monitoring influenza from 2007 to 2009 in Xuhui District Central Hospital were analyzed.The influenza like illness (ILI) incidence and influenza virus isolation from 2007 to 2009 were monitored and analyzed. Results ILI monitoring results showed that in 2007, 1656 cases were ILI, the percentage being 1.20%, in 2008, 1606 cases were ILI, the percentage being 1.12%, in 2009, 5486 cases were ILI, the percentage being 3.10%, significantly higher than those found in 2007 and 2008.Influenza virus monitoring results showed that among 330 samples collected in 2007, there were 45 influenza positive, with the separating ratio 13.6%.The main influenza type was A (H3N2) (68.9%).Among 229 samples collected in 2008, there were 30 influenza positive, with the separating ratio 13.1%.The main influenza type was B type.Among 713 samples collected in 2009, there were 250 influenza positive, with the separating ratio 35.1%.The main influenza type was the influenza A H1N1 (70.8%) and A (H3N2) (20.4%).In August 2009 the main influenza type was seasonal-A (H3N2) influenza virus (58.7%), the influenza A H1N1 (34.7%) viruses, but in December the influenza A H1N1 viruses became the main influenza type (91.4%). Conclusion In summer and winter, there is the peak of the epidemic of influenza in the nearby areas of the sentinel hospital.A (H3N2) was the main influenza virus subtype in 2007 and B type the main influenza virus subtype in 2008.The seasonal influenza A (H3N2) and the influenza A H1N1 influenza pandemic occurred from August to October in 2009, and the influenza A H1N1 virus became the main influenza virus subtype from November to December in 2009.