Abstract: Objective To analyze the infection of pandemic influenza A (H1N1) virus among influenza like illness cases in Changping district in 2009 and provide evidence for the prevention and control of the disease. Methods The nasal pharynx swabs were taken from suspected patients to detect pandemic influenza virus by using real-time reverse transcriptase polymerase chain reaction (rRT-PCR) according to The Guideline of Pandemic influenza A (H1N1) Virus Detection by RT-PCR. Each sample RNA extract was tested by separate primer/probe sets: InfA, Universal swine (swFluA), Swine H1 (swH1) and RNaseP (RP). Results A total 3647 nasal pharynx swabs were detected from 18 May to 29 November 2009, of which 214 were positive for pandemic influenza A (H1N1) virus nucleic acid (5.87%). The first positive sample was detected on 27 July, 112 positive samples were detected during 14-27 September. The cases mainly occurred among the age groups of 5-9, 10-14, 15-19, 20 years old. Students accounted for 76.62% of the total cases. The main symptoms were fever (97.40%), cough (42.86%) and sore throat (31.17%). Conclusion The infection of pandemic influenza A (H1N1) infection mainly occurred among students. The differences on age and population were significant. The detection of nucleic acid of influenza virus would facilitate to find the prevalence of pandemic influenza A (H1N1) virus infection and provide evidence for the clinical diagnosis and prevention/control of the disease.