目的弄清甲３（Ｈ３Ｎ２）亚型流感病毒相变异的分子生物学基础。方法病毒粒ＲＮＡ经逆转录合成ｃＤＮＡ，经聚合酶链反应（ＰＣＲ）扩增，产物纯化，采用双脱氧链末端终止法进行核苷酸序列测定。结果３５株甲３（Ｈ３Ｎ２）亚型流感病毒的ＨＡ１区基因长度均为９８４个核苷酸，它们间无发生任何核苷酸丢失或插入并发现ＨＡ１蛋白分子上氨基酸序列多变点主要在ＨＡ蛋白的顶部，尤其抗原决定簇Ｂ区和受体结合部位（ＲＢＳ），这进一步证实了，ＨＡ蛋白分子上氨基酸替换主要是人群免疫压力所造成。同时还发现了半胱氨酸和脯氨酸具有高保守性及糖基化位点主要集中在ＨＡ１区的Ｎ和Ｃ端，尤其Ｎ端。糖基化位点如此分布在病毒基因进化和流行病学上意义至今不清楚。结论Ｈ３Ｎ２亚型病毒“Ｏ”相毒株的出现与其蛋白分子上第２２６位氨基酸发生替换密切相关并推测“Ｏ”相毒株ＨＡ蛋白三维结构与“Ｄ”相的不同。 Objective To clarify the molecular biology basis of the phase variation of Influenza A (H3N2) subtype influenza virus. Methods The cDNA of virion was reverse transcribed into cDNA and amplified by polymerase chain reaction (PCR). The product was purified and the nucleotide sequence was determined by dideoxy chain termination method. Results The length of HA1 gene of 35 influenza A (H3N2) subtypes was 984 nucleotides. No nucleotide loss or insertion occurred between them and the diversity of amino acid sequence of HA1 protein was mainly found in HA The top of the protein, especially antigenic region B and the receptor binding site (RBS), further confirmed that amino acid substitutions on the HA protein molecule are primarily caused by immune stress in the population. At the same time, it was also found that cysteine ​​and proline are highly conserved and glycosylation sites are mainly concentrated on the N and C termini of the HA1 region, especially on the N-terminus. It is unclear how the glycosylation sites are distributed in the evolutionary and epidemiological aspects of the viral genome. Conclusion The occurrence of the “O” phase of H3N2 subtype virus is closely related to the substitution of the amino acid at position 226 of the protein molecule. It is speculated that the three-dimensional structure of the “O” phase HA protein is different from the “D” phase.