To explore the differences in physiological and biochemical changes of different resistant walnut clones in response to brown spot pathogen infection, we used resistant and susceptible clones as experimental materials. After inoculation with Ophiognomonia leptostyla, the related physiological and biochemical indexes such as protective enzyme activity, total phenol, flavonoids, and chlorophyll content in walnut leaves at different stages were determined. The results showed that: (1) after inoculation, the leaf carrier rates of susceptible clone 64 increased all the time, and was significantly higher than that of diseaseresistant clone 199(P＜0.05). (2) The activities of SOD, POD, CAT, APX and PPO in the leaves of diseaseresistant clone 199 and susceptible clone 64 declined after rising. SOD, POD and APX all reached the maximum on the 16th day. Compared with the susceptible clones, the POD and APX activities of the resistant clones were stronger after inoculation, and the PPO activity of the susceptible clones was higher than that of the resistant clones in the early stage (1~16 d), and the CAT activity in the later stage (16~34 d) was also higher. (3) The leaf chlorophyll content of diseaseresistant clone was always higher than that of susceptible clone; the MDA content of diseaseresistant clones had no significant change after inoculation, while that of susceptible clones increased at first and then decreased, indicating that the cell membrane lipid peroxidation was more serious. (4) The contents of soluble protein and soluble sugar in the leaves of the two clones changed slowly, and the difference was not significant, and there was an increasing trend in the later stage of inoculation (34 days). After 5 days of inoculation, the contents of flavonoids and total phenols in leaves of susceptible clones were significantly higher than those of diseaseresistant clones. It was found that the leaf carrier rate of diseaseresistant clones of walnut was low and it was difficult to be infected. Meanwhile, the ability of disease resistance was improved by increasing the activities of POD and APX and accumulating more chlorophyll, soluble protein and soluble sugar to deal with the oxidative stress caused by pathogen infection and inhibit the reproduction of pathogens.