Abstract: Based on the Mtrix（M）gene sequence of the Swine influenza virus(SIV),a pair of primers were designed and synthesized. By means of it, the RT-PCR technique for detecting SIV was established. The 460 bp specific fragments were obtained subsequently from the Mtrix（M）gene of H1,H3 and H9 subtype Swine influenza viruses. Negative test results were found on the Porcine reproductive and respiratory syndrome virus，Porcine circovirus type 2, Swine pseudorabies virus and Classical swine fever virus. The amplified sequence of PCR product was 99%-100% in agreement with those published data on SIV strains. The sensitivity of RT-PCR reached 103 EID50. The Swine influenza virus could be detected directly from the samples of infected mice ’s lungs.