Abstract: 【Objective】This research aimed to explore the antifungal effect and mechanism of Chinese prickly ash essential oil against Alternaria alternata in tomato，which would provide theoretical reference for the application of Chinese prickly ash essential oil as a botanical fumigant to control A. alternata rot disease in solanaceous vegetable.【Method】Using tomato A. alternata strain HJF-1 as the the tested material，a fumigation experiment was conducted on the mycelium of HJF-1 with different concentrations（40，80，120，160，200 μg/mL）of Chinese prickly ash essential oil and its 3 main components（linalool，limonene and mycrene），with sterile water treatment as the blank control. The antifungal effect of different substances on A. alternata were evaluated. Through microscopy observations，physiological and biochemical analysis and in vitro inoculation methods，further analysis was conducted to study the effect of Chinese prickly ash essential oil and linalool on the mycelial morphology，spore germination，germ tube length，cell membrane integrity and pathogenicity of A. alternata，aiming to clarify the antifungal effect and mechanism of fumigation of Chinese prickly ash essential oil and linalool against A. alternata.【Result】After fumigation with different concentrations of Chinese prickly ash essential oil and its 3 main components，there were great differences in the colony diameter of HJF-1 compared to the control. The inhibition effect showed as Chinese prickly ash essential oil>linalool>myrcene>limonene. The inhibition effects of Chinese prickly ash essential oil and linalool were stronger than those of other components，and the minimum inhibitory concentration（MIC）of the two was both 160 μg/mL. There was significant difference in the inhibition rates of mycelial growth fumigated with different concentrations of Chinese prickly ash essential oil and linalool（P<0.05，the same below）with mycelial growth inhibition rates of 99.10% and 99.00% treated with 200 μg/mL of Chinese prickly ash essential oil and linalool respectively. There was a dose-effect relationship between fumigation concentration and growth inhibition rate of HJF-1，and the half lethal concentrations（EC₅₀）of Chinese prickly ash essential oil and linalool were 85.98 and 89.84 μg/mL respectively. Fumigation with Chinese prickly ash essential oil and linalool not only significantly reduced spore germination rate，but also inhibited spore tube elongation. By fumigation with 200 μg/mL Chinese prickly ash essential oil and linalool for 6 h，spore germination rates were the lowest（1.0% and 1.2% respectively）. At the same time，the lengthes of spore tubes were the minimum（9.2 and 10.8 μm respectively）. In addition，Chinese prickly ash essential oil and linalool could also cause pathogen deformity，cell membrane oxidative damage，and increased mycelium malondialdehyde content to 6.3 and 4.0 nmol/mL after panthogen fumigatied for 12 h compared with before fumigation. By fumigation with the two essential oil for 24 h，the inextracellular soluble proteins contents showed an increase and reached 11.9 and 9.1 μg/L respectively，and a increase in extracellular soluble sugars contents to 263.8 and 237.2 μg/L respectively. At 72 h of fumigation，extracellular relative conductivity reached the maximun，compared with before fumigation which were 62.5% and 50.5%. In vitro experiment indicated that fumigation with Chinese prickly ash essential oil and linalool（2×MIC）for 72 h greatly reduced the pathogenicity of A. alternata with relative control effects of 83.9% and 75.6% to Alternaria rot respectively. Chinese prickly ash essential oil and its main components linalool can block the infection and delay the spread of A. alternata by inhibiting mycelium growth and spore germination，causing intracellular leakage and function disorders through damage of cell surface integrity，and ultimately resulting in reduced pathogenicity of A. alternata.