The Spanish flu first occurred in 1918 and killed about 50 million people in the world. In 2005, by using gene decoding process, Robert B. Belshe identified that the Spanish flu was occurred by H1N1, which is highly pathogenic influenza A virus. Influenza A virus has been mutated consistently and unexpectedly; H5N1, H5N2, and H7N9 which used to be known as not human infecting virus now infect a lot of people in the world. In this research, by using Apriori Algorithm, we compared amino acid strain of Hemagglutinin and Neuraminidase, which are glycoprotein of H1N1, H5N1, H5N2, and H7N9 to figure out their similarity in amino acid strain. Furthermore, in the case of H7N9, we also compared the amino acid data from 1988, 2009 (bird), and 2013 (human) and proposed the significance of biological research about the site which differs in terms of amino acids.