Abstract: The study aims to explore the molecular mechanism of ocimene synthase gene involved in the biosynthesis of volatile compounds of ocimene, and to provide theoretical reference for the cultivation of aromatic varieties of Hemerocailis fulva and Hemerocailis citrina. Using headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and molecular biology methods, the release of ocimene and the expression of bocimene synthase gene in two H.fulva cultivars (‘Zuixiangfei’ and ‘Villa Vanilla’) and two H.citrina cultivars (‘Wupingzao’ and ‘Dingzhuang Dacai’) were analyzed. The results showed that the ocimene content of H.fulva (‘Zuixiangfei’ and ‘Villa Vanilla’) was the highest in blooming stage, reaching 13.9 ng·g^–1 and 692.84 ng·g^–1, respectively, while the content of H.citrina (‘Wupingzao’ and ‘Dingzhuang Dacai’) was the highest in bud stage, reaching 1222.96 ng·g^–1 and 280.52 ng·g^–1, respectively, and their contents were about 124 and 28 times that of H.fulva (‘Villa Vanilla’). After treatment with 500 μmol/L methyl jasmonate (MeJA) solution, the maximum release of H.fulva (‘Zuixiangfei’) ocimene was significantly higher than that of the control group, which was 1.8 times the amount of the control group. The release of ocimene was the highest at 15 ℃, significantly higher than that at 10 ℃ and 20 ℃.Two ocimene synthetase genes were isolated from ‘Zuixiangfei’, ‘Villa Vanilla’, ‘Wupingzao’, and ‘Dingzhuang Daicai’ respectively. Analysis revealed that all members possessed the DDxxD domain, and all except HfTPS-dz1 from 'Dingzhuangdacai' contained the NSE/DTE domain. There was a significant positive correlation between the expression level of ocimene synthase gene and the content of ocimene in petals of Hemerocailis fulva and Hemerocailis citrina, among which the correlation between ‘Dingzhuang Dacai’ HfTPS-dz1 was the lowest. Research results showed that the ocimene synthase gene was involved in the synthesis of ocimene, but its contribution was different among the cultivars.