In order to investigate the effect of exogenous chlorogenic acid on apple gray mold resistance and its own chlorogenic acid synthesis， Fuji apple was treated with 300 μg/mL chlorogenic acid solution for 30 min， and then inoculated with gray mold after 1 d， and treated with water as the control group (CK)， the spot diameter and incidence were counted， and the changes in gene expression and enzyme activity of enzymes related to chlorogenic acid synthesis were determined. The results showed that after treatment with 300 μg/mL chlorogenic acid， the activities of PALC4H and 4CL， the key enzymes upstream of the phenolpropane metabolic pathway， increased significantly， and the corresponding gene expressions all reached the peak after 6 h of inoculation with gray mold， which were 10， 5 times and 2.5 times of the CK group， respectively. Meanwhile， the gene expression of the downstream synthesis gene hydroxycinnamic acid-CoA acid ester/ quinic acid hydroxycinnamic acid transferase (HCT/HQT) reached a peak at 48 h in the treated group， which was about 3 times higher than that in the CK group， and there were two higher gene expressions at 6 h and 12 h in the treated group for coumaric acid 3'-hydroxylase (C3H)， which were about 3 times and 5 times higher than that in the CK group， respectively， stimulating chlorogenic acid synthesis This stimulated the increase of chlorogenic acid synthesis， which induced the increase of fruit resistance， effectively reduced the incidence of apple gray mold and slowed down the expansion of spots. Conclusion: Exogenous chlorogenic acid treatment can induce the response of enzymes of the phenolpropane metabolic pathway， increase the level of chlorogenic acid in apples， and effectively suppress apple gray mold.