To figure out the protective effect of exogenous salicylic acid (SA) on inducing clubroot resistance of pakchoi and the reactions of physiological indicators on susceptible pakchoi plants, with ‘Xinaiqing’ pakchoi as the tested material, after inoculated clubroot disease(Plasmodiophora brassicae Wor) by the method of the soil bacteria inoculation, we investigated the effects of 0.2~0.8 mmol·L^-1 exogenous salicylic acid （SA） on pakchoi plants growth, inducing resistance, reactive oxygen and defense enzyme activities of leaf and root infected clubroot，with the possible action mechanism of SA discussed. The results showed that: (1) the clubroot disease significantly affected the growth and increased the damage of membrane lipid peroxidation. (2) The best effect on the alleviation of clubroot disease stress damage was observed in the treatment of 0.6 mmol·L^-1 SA. At this concentration, the plants growth, resistance of clubroot disease. (3) The activities of superoxide dismutase（SOD）, peroxidase（POD）, ascorbate peroxidase（APX）, polyphenol oxidase (PPO), phenylalanine ammonialyase (PAL), glutathione reductase (GR) were were increased significantly in leaves and roots, while malondialdehyde (MDA), hydrogen peroxide (H₂O₂) contents and the production rate of superoxide anion(O^-·₂) were significantly decreased. The above results indicated that dosage effect of SA existed on the alleviation of clubroot disease stress in pakchoi plants, and the best alleviating effect on clubroot disease stress damage was 0.6 mmol·L^-1 SA by irrigating at the plant roots, which was favorable for the plant to grow, and improve the ability of resistance of clubroot disease.