The nucleotide homology of the HA gene of the 20 strains was 97.7%-100%, which was highly homologous to the vaccinestrains A/Hong-Kong/4801/2014 recommended by WHO in 2017 and A/Singapore-INFIMH/16-0019/2016 recommended by WHO in 2018, but they were significantly different from the vaccinestrain A/Kansas/14/2017 recommended by WHO in 2019. Genetic analysis showed that the 20 strains were divided into two branches, and the strains that were prevalent in 2019 were located in different branches, with marked genetic differences. Key site analysis showed mutations in antigenic determinants A, B, C, and E and mutations in the anterior and posterior walls of receptor binding sites. Key site analysis also showed that there was an increase in the number of glycosylation sites compared with the vaccinestrains prevalent in the same year. Genetic distance, antigen sites, and glycosylation sites were slightly different between virusstrains prevalent in 2017-2018 and virusstrains prevalent in 2019.