Abstract: In this study, a chitinase gene EuCHIT1 from Eucommia ulmoides with a total length of 1 402 bp, including an open reading frame with a sequence length of 969 bp, encoding 322 amino acids. In order to verify the antifungal ability of EuCHIT1, constructed plant overexpression vector pSH-35S-EuCHIT1 was constructed and genetically transformed tobacco to obtain transgenic plants and related experiments were carried out. The results showed that the content of chitinase in transgenic tobacco was significantly higher than that in wild-type tobacco, and the medium supplemented with tobacco crude protein EuCHIT1 had a significant inhibitory effect on the growth of Fusarium oxysporum. EuCHIT1 gene significantly increased the activity of catalase（CAT） in tobacco leaves. In addition, in order to explore the resistance mechanism of EuCHIT1-transgenic tobacco against fungi mold, the expression levels of PR-1a and COI1 were analysed, the key genes in the salicylic acid pathway and jasmonic acid pathway, in transgenic plants and wild types after inoculation with Botrytis cinerea. The results showed that the expression levels of COI1 and PR-1a in transgenic plants were significantly higher than those in wild type plants before inoculation with pathogens. However, the expression of COI1 was inhibited after inoculation with pathogens, and the maximum expression of PR-1a gene in transgenic tobacco after inoculation with pathogens was 33.8 times that of wild-type tobacco. In conclusion, the overexpression of EuCHIT1 gene enhanced the resistance of tobacco to fungi, increased the activity of CAT and the expression of protein genes related to disease course in tobacco plants, and thus enhanced the inhibition effect of plants on Botrytis cinerea and the ability of plants to resist fungus diseases.